Make LocalDatastoreHelper aware of --use-firestore-in-datastore-mode

[ablx]

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Is your feature request related to a problem? Please describe.
I am using Firestore in Datastore mode, yet I cannot correctly emulate it in unit tests since I cannot configure --use-firestore-in-datastore-mode

Describe the solution you'd like
LocalDataStoreHelper should have the possibility to hand over the --use-firestore-in-datastore-mode parameter to the emulator.

Describe alternatives you've considered
Using Testcontainers

Additional context
GoogleCloudPlatform/spring-cloud-gcp#1406

[ablx]

I started to implement it: https://github.com/ablx/java-datastore/tree/949_localdatastorehelper_firestore_in_datastore_mode

However, it does not work. The emulator does not seem to start correctly. If I use the generated prompt directly with gcloud, it works. I cannot see any error logs from the emulator other than below; which is not helpful.

Maybe someone can give me a hint.

com.google.cloud.datastore.DatastoreException: I/O error

	at com.google.cloud.datastore.spi.v1.HttpDatastoreRpc.translate(HttpDatastoreRpc.java:140)
	at com.google.cloud.datastore.spi.v1.HttpDatastoreRpc.commit(HttpDatastoreRpc.java:166)
	at com.google.cloud.datastore.DatastoreImpl$5.call(DatastoreImpl.java:583)
	at com.google.cloud.datastore.DatastoreImpl$5.call(DatastoreImpl.java:580)
	at com.google.api.gax.retrying.DirectRetryingExecutor.submit(DirectRetryingExecutor.java:103)
	at com.google.cloud.RetryHelper.run(RetryHelper.java:76)
	at com.google.cloud.RetryHelper.runWithRetries(RetryHelper.java:50)
	at com.google.cloud.datastore.DatastoreImpl.commit(DatastoreImpl.java:579)
	at com.google.cloud.datastore.DatastoreImpl.commitMutation(DatastoreImpl.java:572)
	at com.google.cloud.datastore.DatastoreImpl.put(DatastoreImpl.java:532)
	at com.google.cloud.datastore.DatastoreHelper.put(DatastoreHelper.java:53)
	at com.google.cloud.datastore.DatastoreImpl.put(DatastoreImpl.java:507)
	at com.google.cloud.datastore.testing.ITLocalDatastoreHelperTest.testCreateWithFirestoreInDatastoreMode(ITLocalDatastoreHelperTest.java:110)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: com.google.datastore.v1.client.DatastoreException: I/O error, code=UNAVAILABLE
	at com.google.datastore.v1.client.RemoteRpc.makeException(RemoteRpc.java:171)
	at com.google.datastore.v1.client.RemoteRpc.call(RemoteRpc.java:117)
	at com.google.datastore.v1.client.Datastore.commit(Datastore.java:87)
	at com.google.cloud.datastore.spi.v1.HttpDatastoreRpc.commit(HttpDatastoreRpc.java:164)
	... 40 more
Caused by: java.net.ConnectException: Connection refused
	at java.base/sun.nio.ch.Net.pollConnect(Native Method)
	at java.base/sun.nio.ch.Net.pollConnectNow(Net.java:672)
	at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(NioSocketImpl.java:542)
	at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:597)
	at java.base/java.net.Socket.connect(Socket.java:633)
	at java.base/sun.net.NetworkClient.doConnect(NetworkClient.java:178)
	at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:498)
	at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:603)
	at java.base/sun.net.www.http.HttpClient.<init>(HttpClient.java:246)
	at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:351)
	at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:373)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1309)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1242)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1128)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:1057)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getOutputStream0(HttpURLConnection.java:1430)
	at java.base/sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:1401)
	at com.google.api.client.http.javanet.NetHttpRequest.execute(NetHttpRequest.java:113)
	at com.google.api.client.http.javanet.NetHttpRequest.execute(NetHttpRequest.java:84)
	at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:1012)
	at com.google.datastore.v1.client.RemoteRpc.call(RemoteRpc.java:97)
	... 42 more