Migrate Java repos full to release-please and release-trigger

Need to set `handleGHRelease: true` 

- [x] java-shared-config
- [x] java-shared-dependencies
- [x] google-cloudevents-java
- [x] java-cloud-bom

then:
- [ ] remove `java` from the `tag` and `trigger` allowlists

This fully decouples release-please from the triggering of Kokoro jobs