Add protoc recipe to cerbero for gst-plugins-rs webrtc livekit signaller

If gst-plugins-rs!1262 (merged) lands and we want to build it in cerbero we'll need the protoc tool.

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The following discussion from gstreamer!4960 (closed) should be addressed:

• @tpm started a discussion: (+2 comments)

  Shouldn't this be added here instead? https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/blob/main/ci/windows-docker/Dockerfile