Different reviewers for different target repos

[ataylormays-duetto]

I'm syncing a file from repoA to repoB and repoC and I want those two repos to have separate reviewers, but there's no way to do that with the action. Since the reviewers are specified on the action, the same reviewers are assigned on each target repo.

A couple implementation ideas:

• If the sync.yml allowed us to specify reviewers then this would be possible
• Alternatively allowing a mapping of reviewer->repo in the action would also work

[shaharkedar]

I created this PR to address this request:
#352