Switch to app based GitHub auth in VMR sync pipelines

We should switch the VMR synchronization pipelines to use a KV + GitHub app just like we did in this repo:
#6394

The sync pipelines are here:

we ended up reverting back to PATs.
The authentication in the darc versions we have pinned in sdk and installer doesn't support installation tokens
We created one specialized PAT for the vmr sync pipeline that we'll own