Don't fail incident creation if creation of collab doc falis

This changes Corto.CreateIncident to treat everything but the Phab ticket creation as best-effort. Additionally, creation of the Google Doc, and templating & storage of the comment are now ran in the background (I've seen these steps add significant latency to the command).

This isn't 100% ideal; Any errors for these best-effort (and now async) operations will be lost.

One option would be to return some sort of compound result set. A structure that could return all of the various successes and failures to the caller. Another would be to change the abstractions and move logging into Corto. My preference here would be for the latter, but only after we transition Corto to a service (at which point an irc bot is a mere client that doesn't need this sort of specificity).

For now, I think this is Good Enough™ (and it is easy/straightforward).

Bug: T379858