docs: began merging variant client samples

[craiglabenz]

This comes as part of an effort to consolidate the firestore_setup_client_create and firestore_setup_client_create_with_project_id regions.

[snippet-bot]

Here is the summary of possible violations 😱

There is a possible violation for not having product prefix.

• samples/snippets/src/main/java/com/example/firestore/Quickstart.java:72, tag fs_initialize

The end of the violation section. All the stuff below is FYI purposes only.

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Here is the summary of changes.

You are about to add 3 region tags.

• samples/snippets/src/main/java/com/example/firestore/Quickstart.java:47, tag firestore_setup_client_create
• samples/snippets/src/main/java/com/example/firestore/Quickstart.java:68, tag firestore_setup_client_create
• samples/snippets/src/main/java/com/example/firestore/Quickstart.java:72, tag fs_initialize

You are about to delete 2 region tags.

• samples/snippets/src/main/java/com/example/firestore/Quickstart.java:50, tag fs_initialize
• samples/snippets/src/main/java/com/example/firestore/Quickstart.java:51, tag firestore_setup_client_create

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[craiglabenz]

CI appears to be upset that I moved a pre-existing region tag?

[kolea2]

LGTM, I think the region tags look fine. I think it's warning about the format of fs_initialize, but since this already exists we should leave as is for this PR.

[craiglabenz]

For posterity, the new snippet looks like this:

// Option 1: Initialize a Firestore client with a specific `projectId` and
//           authorization credential.
FirestoreOptions firestoreOptions =
    FirestoreOptions.getDefaultInstance().toBuilder()
        .setProjectId(projectId)
        .setCredentials(GoogleCredentials.getApplicationDefault())
        .build();
Firestore db = firestoreOptions.getService();

// Option 2: Initialize a Firestore client with default values inferred from
//           your environment.
Firestore db = FirestoreOptions.getDefaultInstance().getService();