Always add current user to autocomplete controller to support filter by "Me"

### What does this MR do?

This MR always adds the current user to the autocomplete list of users.

### Why was this MR needed?

Normally only the members from a team or the group are shown in the autocomplete list. However, this prevents a user from filtering issues belong to him/her if the user does not belong directly to either. To make this filtering more usable, we can be sure to add the current user to the list, which the JavaScript code will move to the top of the list.

### What are the relevant issue numbers?

Partial fix #2202

See merge request !1100