[MS connector] Garbage collection

[tdraier]

Implement garbage collection : remove indexed resources that do not exist anymore

[philipperolet]

codependency with #6290

[philipperolet]

Theoretically, garbage collection is not needed since deletions are picked up in incremental syncs In practice, a sanity check that each node is still live would give us a stronger guarantee:

• perpetually running workflow microsoft-{connId}-garbageCollector
• check all nodes in our connectors' table are still live
• spread the check at 1qps and max once per day, to avoid oversollicitation of ms api With this rate a 200,000 item drive would be fully garbage collected in less than 2 days
• optional: limit the check to items unseen for more than a week

Add the garbage collect workflow to monitoring

[philipperolet]

Note: while garbage collection flow is not theoretically required, deletion code is, and should be written when folders are deselected from add/remove resources