[Enhancement] - Cases, but they can be Slack channels

[wssheldon]

Summary

A highly requested feature is for Cases to support dedicated channels, just like Incidents do today. This PR adds that functionality. We refactor some functions to use the Subject pattern, so that they work for both incidents, and cases. Notably, (Bookmarks and Announcement Messages).

When a dedicated channel Case is escalated to an Incident, we reuse the Conversation object for the new Incident. There was already a conditional in create_incident_resources that only created a conversation if one did not exist on the incident object, so we leverage this, and it worked seamlessly. Case channels are prepended with case- so that they are not ambiguous. The channel is renamed on escalation to the new Incident name and the case- is naturally removed at this point.

We add some Slack /slash commands to make the Case dedicate channel experience better. Allowing you to update cases and escalate them directly in Slack.

Miscellaneous Changes

• We remove the participant announcement messages on Incident creation and replace them with a "bulk" version, that sends one message, with the number of participants added, and their cards.
• We refactor the triage_flow for cases to use a match statement to improvement readability.
• We add tooltips to the Case page for all resource icons, the private icon, and the escalate icon.
• We truncate the description on the Case Type dropdown on the Case report form.

[wssheldon]

@mattsta Why the confused emoji?

[mattsta]

oh, sorry, I didn't realize homepage reactions are actually issue reactions. didn't expect anybody to see it outside of the promo box itself (I always thought the home feed reactions were in their own isolated universe somehow?).

initial reaction was more "cases are sad to have, wish everything just worked." i'd also disagree with it being "confused" emoji as they have it labeled? never noticed that was its official title before. always thought it was more "sad / sorry / condolences" but who knows.

I think per-case channels are a great idea though. Much better than the CEO dropping into #engineering with WHY IS THE WEBSITE DOWN then starting a secret video chat without any historical trace of troubleshooting progress and participants when new contacts/departments/helpers need to be brought in mid-event. 👍

[wssheldon]

@mvilanova @whitdog47 @metroid-samus Ready for review now if you'd like to take a look.