Fix routing header issue in Firestore Beam connector

[pl04351820]

Fix routing header issue in Firestore Beam connector

• Populate x-goog-request-params header so that Beam connector can access the named databases.
• Re-enable the Firestore Beam integration tests after fixing the header issue.
• Addressed [Failing Test]: Firestore integration tests failing affecting GCPIO_PreCommit, DataflowPostCommit V1 and V2 #25851.

The change is tested via

$ ./gradlew integrationTest -p sdks/java/io/google-cloud-platform -PgcpProject={project-id} --tests=org.apache.beam.sdk.io.gcp.firestore.it.FirestoreV1IT  --stacktrace

[github-actions]

Assigning reviewers. If you would like to opt out of this review, comment assign to next reviewer:

R: @bvolpato for label java.
R: @ahmedabu98 for label io.

Available commands:

• stop reviewer notifications - opt out of the automated review tooling
• remind me after tests pass - tag the comment author after tests pass
• waiting on author - shift the attention set back to the author (any comment or push by the author will return the attention set to the reviewers)

The PR bot will only process comments in the main thread (not review comments).

[bvolpato]

LGTM, thanks!

[github-actions]

R: @kennknowles for final approval