Support manual Protobuf update process

[scruplelesswizard]

This re-enables the update process originally used for protobufs, lost in #4805

[scruplelesswizard]

The workflow from #4805 did not trigger when tested in in #4818. Github Actions doesn't appear to traverse the submodule, making the paths filter on protobufs/ effectively never().

This PR also updates the paths filter to .gitmodules. This has the side-effect that the workflow will trigger every time the meshtestic submodule is updated as well. This may cause the EndBug/add-and-commit when there are no files to add, the documentation appears inconsitent on the behavior.