[PiranhaJava] Update sample project to show option for excluding additional EP checks

In the past we have made PR's to Piranha to support additional usage patterns.

While integrating Piranha with multiple java micro services in our organisation, we are noticing lots of Error prone reported violations on our micro-service project and it becomes a hard dependency to fix the violations before integrating Piranha.

For new projects, we can add Error Prone as a dependency from beginning and get going. But for existing services, fixing the error prone violations is becoming hard.

Question:

1. is it possible to run Piranha without Error Prone as a mandatory dependency in build system?
2. If not, is it possible to suppress the Error Prone violation as warning instead of build errors?
3. iI it possible to exclude specific packages from Error Prone scan? (Like available configurations available in Jacoco/find bug and so on)