HHH-19983: Config for running tests on Spanner emulator

[rayudu3745]

This change introduces the initial setup required to execute Hibernate Spanner Dialect tests against the Cloud Spanner Emulator:
https://github.com/GoogleCloudPlatform/cloud-spanner-emulator

With this configuration in place, Spanner Dialect tests can now be executed locally by running:

./docker_db.sh spanner

./gradlew test -Pdb=spanner

At present, the test suite will not pass. There are multiple known gaps and incompatibilities in the current SpannerDialect implementation that prevent full test coverage from succeeding. These issues are expected and will be addressed incrementally in upcoming PRs, which will deliver fixes, behavioral corrections, and broader functional improvements.

This PR focuses solely on enabling the emulator-backed test environment so that future development and validation can occur consistently and locally.

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https://hibernate.atlassian.net/browse/HHH-19983

[sebersole]

@beikov As the docker / container expert, wdyt?

[beikov]

This looks good already, but I wonder if we can enable parallelization as well, as I assume that the emulator will be "slower" probably?
Since databases are automatically created (apparently?), it might be as simple as changing the JDBC URL to jdbc:cloudspanner:/projects/orm-test-project/instances/orm-test-instance/databases/orm-test-db-$worker?autoConfigEmulator=true;lenient=true and adding the name of the database bundle to the if checks in hibernate-core.gradle and hibernate-envers.gradle. Search for GradleParallelTestingResolver in those files and you will find the place.