spanner: allow user-agent to be passed in and not a hardcoded version

[odeke-em]

We'd like to be able to pass in a user-agent from applications that build atop spanner-ruby (we are currently building an ORM plugin),
where ideally the final user-agent when set by us would be

x-goog-api-client': \
'spanner-activerecord/0.0.1 gl-ruby/<VERSION> grpc/<gRPC_VERSION> gax/<GAX_VERSION>' 

Coming here from a report by @jiren on January 19th 2020, which I shall quote verbatim:

@odeke-em In ruby spanner this is not possible as per current implementation. Ruby spanner lib has hardcoded values.

lib_name: "gccl",
lib_version: Google::Cloud::Spanner::VERSION

Here is the file link,

google-cloud-ruby/google-cloud-spanner/lib/google/cloud/spanner/service.rb

Lines 54 to 55 in fe8f239

	lib_name: "gccl",
	lib_version: Google::Cloud::Spanner::VERSION

I think need to create an issue on spanner ruby.

This issue is to follow up with @jiren's report. /cc @skuruppu

[quartzmo]

@odeke-em Thanks for this request. @jiren Do you want to take this?

[jiren]

@odeke-em Thanks for this request. @jiren Do you want to take this?

Yes @quartzmo , I have created pull request against this.

[skuruppu]

Thanks to @quartzmo, #4762 is now in google-cloud-spanner 1.14.0. Closing this issue.