ci: static analysis for java

## Issue
Add some check-style or other check similar to the flake8 checks we've added for python.

## Suggestion 1
Apache Beam is always "a little weird" in style so I think a good starting point would be to steal this [checkstyle.xml](https://github.com/apache/beam/blob/d577e41f96f00b2d9b69af9b1d09f2850a9d1f09/sdks/java/build-tools/src/main/resources/beam/checkstyle.xml) as a starting point.

Note it seems [some existing java assets](https://github.com/GoogleCloudPlatform/professional-services/search?q=checkstyle.xml&unscoped_q=checkstyle.xml) might already use beam's checkstyle

### Watch point
we should test that this plays nicely with the existing [google-java-format](https://github.com/google/google-java-format) standard (note beam uses [spotless](https://github.com/diffplug/spotless)) in this repo to avoid issue similar to flake8 v.s. yapf in #468 .