Run checkstyle in CI

[mccheah]

I noticed that it's possible to make a formatting error, such as disorganize imports or change indentation, without ./gradlew check noticing. This issue proposes adding more rigorous checkstyle and code linting integration to this project.

An idea is to use the baseline toolkit, but we can also write the linting configuration by hand.

[rdblue]

How are we doing on this? Most modules are running checkstyle, right?

[mccheah]

This can probably be superceded by all the individual tasks for Baseline integration.

[rdblue]

Thanks! I'll close this.