fix(admin): searcher issues

Description

fix(admin): searcher issues

• Properly chosen default searching VO.
• Properly chosen default searching attribute.
• Fixed spinner.
• Virtual attributes are hidden.

How to test

Open the Searcher and check that individual issues from the assignment were fixed.

Author's checklist

• I have followed the contribution guidelines
• This MR has been tested or does not change functionality
• I have added relevant merge request dependencies (if this MR has any)
• I have added the correct labels
• I have assigned reviewers (if any are relevant)
• I have edited the documentation (if the changes require it) or I have noted the need for the change if I do not have access to the documentation
• I have marked all introduced BREAKING CHANGES or necessary DEPLOYMENT NOTES in the commit message(s)

Reviewer's checklist

• This MR has been tested or does not change functionality
• This MR has correct commit message format

Other information

Related MR: perun!4350 (merged)

Related issues

re STR-1224