Bazel doesn’t provide any way to propagate certain build rule variables across many targets automatically.

The current issue is, if we want to set `copts= “-Isrc”` for all targets under the /src/ directory, we would have to set it in every single target manually.

Since we likely are going to need to add other custom settings beyond copts, create a custom build target for each target type (lib, cc, etc) that every other build rule can depend on where we can add custom mongo settings, like copts.

See https://docs.google.com/document/d/1e2A1M8yjSTwxOtEB9As1XwfjSuUlmiXVSQFfl3b_FaU/edit