[darc/maestro++] Allow specifying additional ignoreChecks to the standard merge policy

[riarenas]

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

The standard merge policy in Maestro is defined as:

The standard github merge policy is:
- AllChecksSuccessful with the 'WIP', `build analysis`, and 'license/cla' checks ignored.
 - NoRequestedChanges
 - DontAutomergeDowngrades
The standard Azure DevOps merge policy is:
 - AllChecksSuccessful with the 'Comment requirements', 'Minimum number of reviewers', 'Required reviewers', and 'Work item linking' checks ignored.
  - NoRequestedChanges
  - DontAutomergeDowngrades

When repositories add checks to their PRs that should be ignored by Maestro, they lose the option of using the standard merge policy, and have to manually add all three policies to all of their subscriptions / branches. It would be useful if the standard policy allowed the addition of checks to ignore, like we do when using the AllChecksSuccessful policy individually.

[michellemcdaniel]

Feels like this should go into one of the Maestro/darc improvement epics?

[premun]

This one started to be a problem the SDK team is hitting. I think we should implement this.

[dkurepa]

This was added in the PR above. It has the same behavior as all checks succeeded