Ensure renovatebot generates changesets as well

[mvgijssel]

Running a command after renovate is done only works with a self-hosted Renovatebot https://docs.renovatebot.com/self-hosted-configuration/#allowpostupgradecommandtemplating.

TODO

• Support passing an argument to bazel run //:release_manager.generate
• filter out release manager files when checking a diff (for Bazel-diff, bazel-differ and files-changed)
• Include bazel run //:release_manager.generate in the BuildBuddy "Release all targets" step
• Enable global renovateapp

[mvgijssel]

With the new version of rules_pycross it might not be necessary anymore to run a custom Renovatebot! We just need to generate changesets if the "triggering user" if Renovatebot. What we can also do is always run bazel run //:release_manager.generate within the release step in the CI and pass in the title of the PR to be used as the changeset body!