MR Process: Create a simple grunt task for patching one maintenance branch

[zepumph]

From a conversation with @samreid.

Like cd density; grunt maintenance-cherry-pick --dependency=density-buoyancy-common--sha=SHA --branch=1.2

This is basically an alias for:

    await m.createPatch( DEPENDENCY, 'for rc.2', patchName );
    await m.addPatchSHA( patchName, sha );
    await m.addNeededPatch( 'REPO', '1.2', patchName );
    await m.applyPatches();
    await m.updateDependencies();

[zepumph]

One important part of this change would be modulifying the .maintenance.json so that we didn't blow away a central one on each grunt command. Likely what would be best here is to just use a maintenance state that is never written, and just lives in memory.