Incompatible flag diff script

[philwo]

Sometimes, people flip incompatible flags, but forget to update the GitHub issue. The release manager then has to go through all flags manually and check their real status.

@laurentlb Had the following idea:

What do you think of a script to diff the incompatible flags between two Bazel binaries? If we run "bazel help" and collect the flags, we can print which flags: have been added, removed, and flipped since the previous release. This can be useful for the release manager.

Sounds good. We should then also integrate it into the release playbook as a step.

[fweikert]

There's bazel help flags-as-proto if you don't want to parse unstructured text. The default flag values have to be added to https://github.com/bazelbuild/bazel/blob/master/src/main/protobuf/bazel_flags.proto, but that' trivial.