Retry on slack failures

[KatieMSB]

Describe the Bug:
When updating User Groups for on-call schedule notifications, if Slack returns an error, the following message is posted in the schedule's on-call notification Slack channel:

Hey everyone! I couldn't update @<user_group> because I ran into a problem. Maybe touch base with the GoAlert admin(s) to see if they can help? I'm sorry for the inconvenience!

Here's the ID I left with the error in my logs so they can find it:
SlackUGErrorID=<service_id>

This behavior occurs when encountering a fatal_error response from the Slack API. We should implement retry logic in this scenario, or at least offer the user an option to manually trigger a retry.

Expected Behavior:
GoAlert should either automatically retry the request when encountering a fatal_error response from Slack or provide users with the option to trigger a retry within the error message.

Application Version:
All versions as of v0.33.0

[mastercactapus]

Let's handle this as part of the job queue transition -- we'll get easier retry logic that way for free, and can have the final error (if it fails) show up with this message.

The main complexity today is I don't think today's system has a way to know "is this the final try?" so if the group update call fails it "falls-back" to sending a message, and marked it as delivered if that works. We should instead implement something where it only trys to update the user group, and if that fails the max-try times, schedule a separate job to send the error message (which can then retry)