Show work items with epic type in issues autocomplete at project level

When typing # in a comment (or description) of an issue we trigger an autocomplete dialogue with a list of work items in the issue's project but work item epics are omitted because they are defined at group-level.

Currently, we need to use the legacy reference & to trigger the epics autocomplete in an issue, but it should be available as part of the work items autocomplete.

Proposal: Work items with type Epic should also be included in the autocomplete triggered by # in an issue.

Given the existing performance issues for this trigger, we want to address Optimize autocomplete of items in issues table (#289238 - closed) because we can introduce a new type to the list.