We used to wait until all work in the admission webhook was done to save
out the new list of streams as edited by the webhook. This produces two
issues:
1. It was possible to encounter a race condition if a second webhook
fired while the first was still processing the callout to Discord
2. If the webhook throttle engaged, `handle_notify()` would return
before saving the list out at all
Now we inspect the list, decide what we're going to do, save the new
list out, and then call the Discord webhook as appropriate.
There's a one-second sleep in the old hook, because the Oven API did not
always record the stream change quickly. Sometimes even that was not
enough. This attempts to work around that by managing the stream list
directly.
10,000 hours mucking with `git filter-repo` and no reasonable use-case
found. On the plus side, anyone looking at this and curious what I nuked
isn't missing much. This lived in a monorepo up until about a week ago.
