[darc/maestro++] Add option to use direct merge instead of PR for subscriptions / repo merge policies

[riarenas]

• This issue is blocking
• This issue is causing unreasonable pain

Introduce an option for repos to opt in into skipping dependency update PRs, and instead have Maestro merge the dependency updates directly into the target branch after testing things out with an official build of the repo.

This should happen at the subscription level for non-batched subscriptions, and at the repository-branch policy level for batched ones.

[riarenas]

We closed the epic this was related to as we don't think it's a good idea to proceed with this work. This was left dangling.