chore: remove java-common-protos/.kokoro and enable renovate bot for requirements file.

[mpeddada1]

Fixes #1485

Notable changes:

• Removed java-common-protos/.kokoro which was carried over from the repo's migration to the gapic-generator-java repo.
• Unpins dependencies in .kokoro/requirements.txt. Similar to the changes applied in chore: Upgrade to later version of gcp-uploader and protobuf synthtool#1741, now that our jobs have been upgraded to Python 3.9, we no longer have to pin the dependencies in requirement.txt.
• Enables renovate bot to update requirements.txt when new version is found. We are currently managing the versions in the requirement.txt file manually (unless there is a dependabot security update). See chore: update gcp-releasetool to 1.10.5 #1370.

[suztomo]

We don't use java-common-protos/.kokoro. (Let me know if you think otherwise)

Would you add a check (either this PR or another PR) to ensure these requirements files can be installed. It's great if we can use the same container image as we use in the release job.

[mpeddada1]

We don't use java-common-protos/.kokoro. (Let me know if you think otherwise)

Not sure if this is expected but I see that the nightly and presubmit jobs are still running but the release jobs haven't been executed since Nov, 2022. Does that mean that the .kokoro/release scripts for java-common-protos can be removed?

UPDATE:
Looking at the build log, these jobs are running for the old repo.

Would you add a check (either this PR or another PR) to ensure these requirements files can be installed. It's great if we can use the same container image as we use in the release job.

Sure! I'll work on adding the check in.

[mpeddada1]

@suztomo I've removed the .kokoro directory from java-common-protos and added a check for requirements.txt. Could I get another review from you?

[suztomo]

Great. Can you also add check to confirm releasetool module import?

• https://github.com/googleapis/gapic-generator-java/blob/main/.kokoro/release/stage.sh#LL23C3-L23C25
• https://github.com/googleapis/synthtool/blob/master/docker/owlbot/java/container_test.yaml#L36

[suztomo]

Thank you. Merge once all are green.

[sonarqubecloud]

[gapic-generator-java-root] Kudos, SonarCloud Quality Gate passed!   

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[sonarqubecloud]

[java_showcase_integration_tests] Kudos, SonarCloud Quality Gate passed!   

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0 Security Hotspots
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No Duplication information

[sonarqubecloud]

[java_showcase_unit_tests] Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information