feat(generator): identify mono repo from config instead of len

[zhumin8]

Before this change, monorepo is identified by length of libraries section in generation_config.yaml. This change makes it explicitly declared as a field in generation_config.yaml

google-cloud-java config change needs to merge first: https://github.com/googleapis/google-cloud-java/pull/11478

BEGIN_COMMIT_OVERRIDE BEGIN_NESTED_COMMIT chore: update repo-level parameter monorepo to True END_NESTED_COMMIT END_COMMIT_OVERRIDE

[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

[zhumin8]

obsolete