Slack context in Sentry issue

### Problem Statement

We leverage the Slack integration to notify us about new / regressed issues (and the recent Slack integration updates have been great, specifically the UX change around threading re-opened issues). We often find ourselves dropping a comment on Sentry issues with a link to relevant Slack threads that contain historic triage context. This facilitates future triaging should the issue regress, but given the manual process, people often forget to create this bi-directional relationship.

### Solution Brainstorm

It would be great to expose Slack message / thread links somewhere in the Sentry issue page itself.

Alternatively, the comments themselves could sync bi-directionally as described in https://github.com/getsentry/sentry/issues/71175.

### Product Area

Issues