RFC: Turn down PagerDuty notifications in #support_self-managed

Request for comments

Need

PagerDuty notifications are currently sent to the Slack channel #support_self-managed. Due to the increase in the number of emergencies, this channel is now dominated by PagerDuty-related messages, which makes it harder to use the channel for discussing other non-emergency topics related to self-managed GitLab. Presently, I've noticed that messages from SEs in the channel have low or no engagement, and I suspect this is because of the volume of PagerDuty notifications.

Approach

We should turn off notifications in the #support_self-managed channel. Notifications are already also sent to #spt_on-call, so we should use this channel for emergency collaboration instead.

Benefit

The #support_self-managed channel will be easier to use and communicate in. This will return the channel to its intended purpose of collaborating on non-emergent self-managed GitLab tickets.

Competition / Alternatives

I'm not sure if this is possible, but "turning down" the amount of notifications from PagerDuty might also be useful. Rather than sending a message for all updates to an emergency, choosing to send only the most important notifications may offer a decent compromise.