Support a DARC subscription frequency that varies by the type of change

[MichaelSimons]

With the introduction of the VMR, I would l like a subscription frequency that varies based on the type of changes.

For backflow PRs from the VMR to the product repos I want the following behavior:

• If the change is to a repo's dependencies - flow the changes once a week.
  • This includes arcade updates (e.g. eng/common).
• If the change is within the repo's src - flow the changes on EveryBuild.
  • When triggered, it would also include any un-flowed dependency changes.

The motivation behind this ask is to:

• Reduce the "noise" from dependency only flows.
• Flow any code changes immediately in order to validate the changes made in the VMR ASAP.

Today there is no mechanism to achieve both these goals as they are in conflict with each other with the currently supported update frequencies.