Resolve "Show a message when loading the issues / merge requests dashboard without filters"

What does this MR do?

Checks if at least one filter is set when listing issues/MRs on dashboard page. It also switches from username to user id in the search autocomplete widget, this assures that user is preselected in the dropdown filters on dashboard issues/MRs page.

Screenshots

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend

What are the relevant issue numbers?

Closes #43246 (closed)