Add filter to GET partner-access endpoint

[eleanorreem]

I had a request to check multiple access codes to see why they weren't working. Instead of spending the time manually looking at each entry - I decided to update the GET endpoint to check them as it only would have taken a little longer than the manual checks and writing the SQL.

• adding an optional filter object to the GET partner-access endpoint. It will remain superadmin authguarded
• 2 service tests to safeguard the endpoint
• This potentially might be useful for our new partner access update UI as well