chore: setup declarative configuration for branch protection and release-please

[zhumin8]

fixes #3085

This change should migrate all required tests from "settings" tab to .github/sync-repo-settings.yaml. Also setting up release-please branches for lts.

Sync-repo-settings.yaml is updated referencing this guide, and settings in google-cloud-java here.

Release-please.yaml is updated referencing this and google-cloud-java settings here.

Questions to reviewers:

• Is permission rules with "yoshi-" teams still accurate? Do we prefer java specific teams as admin/push?
• This update will override configurations in “Settings” for protected branches, I do not have access to this tab. Can you please double check I am not missing anything AND/OR give me access to it?

[sonarqubecloud[bot]]

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

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarqubecloud[bot]]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarqubecloud[bot]]

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

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud[bot]]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud