Persist Zoom meetings added to issues in the database

In #31103 (closed) we've added /zoom and /remove_zoom quick actions in order to add (or remove) a Zoom meeting to an issue.

In #31103 (comment 216346393) we've decided to keep storing a Zoom meeting URL in the issue description. This is not ideal for several reasons:

• Users see the attached Zoom URL in the issue description.
• Users can implicitly add/remove Zoom URL by tweaking the issue description.
• Adding a Zoom URL and checking whether a Zoom URL is present or not is cumbersome.
• Adding meta information to the Zoom meeting (e.g. its status) is not feasible.

Proposed solution

Track Zoom meetings associated with an issue in the database.