Related epics adds `#` when entering an ID

Problem

A customer recently reported:

would prefer a hover-over or question mark button as the flow isn’t obvious. Anything that isn’t obvious they are going to skip over it and won’t read the documentation

One potential root cause:

1. The search + autocomplete does not work unless you first type &.
2. As we are re-using the components from issue linking, when you start typing, it automatically injects # into the search string to get auto-complete to work without having to first type #.
3. Given we're linking epics here, injecting # is not helpful.
4. Actually finding the epic you want to link, selecting the URL, copy + paste, then clicking Add is a cumbersome, multi-step process that is inefficient.

Other Thoughts

• We may want to update https://docs.gitlab.com/ee/user/group/epics/linked_epics.html#add-a-linked-epic to let folks know that autocomplete also works for searching the title of the epic, so you don't necessarily need to know the ID. (We should fix having to type & in order to trigger the autocomplete. It should just trigger when you start typing)