Feature request: add darc command to find which repo/branches consume a given repo/branch

- [ ] This issue is blocking
- [ ] This issue is causing unreasonable pain

Users would like the ability to ask "given this repository and this branch, which other repo/branches consume the output."

This should be pretty straightforward:

1. Get all the default channels for a given repo at the branch
2. Look up all the subscriptions for the default channels and given repo.
3. Report back the repos and branches that are output.

Teams discussion: https://teams.microsoft.com/l/message/19:afba3d1545dd45d7b79f34c1821f6055@thread.skype/1677015952798?tenantId=72f988bf-86f1-41af-91ab-2d7cd011db47&groupId=4d73664c-9f2f-450d-82a5-c2f02756606d&parentMessageId=1677015952798&teamName=.NET%20Core%20Eng%20Services%20Partners&channelName=First%20Responders&createdTime=1677015952798&allowXTenantAccess=false

### Release Note Category
- [ ] Feature changes/additions
- [ ] Bug fixes
- [ ] Internal Infrastructure Improvements
### Release Note Description