Move existing search filters for Issues and MRs to left sidebar in global search results page

Problem to solve

Users need additional ways to narrow their search results to aid in finding the information most relevant to what they are looking for.

We have started by providing filters for status (#237932 (closed) & #237938 (closed)) and confidentiality (#238314 (closed)), but as we continue to build out these facets we need to adapt the results layout to accommodate these facets more effectively. This issue introduces a new sidebar within the search results page dedicated to these facets.

Proposal

Start by moving the current filters for Issues and Merge Requests into a new facets sidebar on the search results page.

The backend currently supports only single selections for these facets at this time, so we will expose these as radio options until multi-selection is available.