We want to support to rendering (done) and edit (new) all issue field types.

With special case for User type.
User field (like assignee, reporter) and rich text fields like description, environment, comments will have configurable pool of users that can be used.

The “Pool” configuration will be done in security tab.
Pool options:
- All users (default off)
- Users from ticket* (default on)
- Selected users (multi-select) (default off)

* Users from ticket - users that are already somewhere on the ticket as a field, or there they are comment authors. Or already they are mentioned in rich-text (description, environment, comment).

All of those options can be enabled:

We do not want to expose autocomplete for all users by default (that would be problem from security standpoint).
That is why only users that “Users from ticket“ are by default.