Migrate build system to bazel

(basing this on #2)

What are people's thoughts on migrating this repo to use bazel instead of maven? Not only would it match the build tooling that envoy uses, but it would also simplify the problem of importing the necessary protos, as we'd be able to depend on data-plane-api instead of copying all the protos into this repo. Bazel also has fairly good native support for Java and the IJ plugin works well for small repos.

Thoughts? I'd be happy to put in the work to move it over (I have some experience migrating java repos to bazel), but I'd like to know where we stand on this before starting that work.