Update the bazel docs for bzlmod and gazelle integration

[udf2457]

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The doc page for bazel is nice, but it needs updating from two perspectives:

1. WORKSPACE is now considered legacy, and bazel is now recommending bzlmod, i.e. MODULE.bazel. The docs should really be updated to reflect this.
2. Most real-world projects use gazelle to automatically find files and create local BUILD files.

I have been bashing my head against a wall trying to get bazel to work in conjunction with bzlmod and gazelle to compile some gRPC stubs into Go from some proto files. I have been unable to find an end-to-end example that uses both, most examples use WORKSPACE and the few that use bzlmod don't show how to integrate with gazelle !