Doc: render references to Message/RPC from comment

[sluongng]

In the Bazel ecosystem, our proto files are heavily commented.

Fields, Message, RPC comments often reference to other namespace with syntax like this:

// The action cache API is used to query whether a given action has already been
// performed and, if so, retrieve its result. Unlike the
// [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage],
// which addresses blobs by their own content, the action cache addresses the
// [ActionResult][build.bazel.remote.execution.v2.ActionResult] by a
// digest of the encoded [Action][build.bazel.remote.execution.v2.Action]
// which produced them.
// ...
service ActionCache {
...
}

is it possible to render these references properly in Buf's module documentation?