fix: adjust release-please configs for cloudbuild yaml updates

[mpeddada1]

Following the Update arbitrary yaml file strategy is resulting in release-please making unexpected changes to the cloudbuild yaml files. See #2350.

Modifying release-please configs to follow Update arbitrary file strategy combined with inline annotations as described in https://github.com/googleapis/release-please/blob/main/docs/customizing.md#updating-arbitrary-files:

[burkedavison]

Should there be associated x-release-please-version comments added to the cloudbuild files, as mentioned in the screenshot for this PR?

[sonarqubecloud]

Quality Gate passed for 'gapic-generator-java-root'

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
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No data about Duplication

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate passed for 'java_showcase_integration_tests'

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[mpeddada1]

Should there be associated x-release-please-version comments added to the cloudbuild files, as mentioned in the screenshot for this PR?

Hmm yeah was thinking about this too. We have the x-version-update annotation which is slightly different from the ones listed in the readme but is the convention in most our repos including java-shared-config (which uses it to update the cloudbuild yaml files) so was curious to try this out as an initial attempt.