[Gitlab Integration] Surface an error message when Gitlab loses connection to Sentry

### Problem Statement

When the account that set up the Gitlab integration with Sentry is no longer active on Gitlab, our integration on Sentry sides starts failing with no relevant error messages. We do not provide information that the connection has been broken in the UI and it can be very confusing for other users of the org

### Solution Brainstorm

- We should at least add an error message in some way when the connection is lost.

- On top of an error message, ideally we could provide users a way to update the credentials attached to the Gitlab integration, so they do not have to wait for a deletion queue and set up from scratch

### Product Area

Settings - Integrations