improve agent mappings page

[EddeCCC]

Add progress spinner for AgentMapping-UI and cache agent mappings

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This change is 

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (986a6bb) 78.53% compared to head (64b1688) 78.54%.
Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1639      +/-   ##
============================================
+ Coverage     78.53%   78.54%   +0.01%     
- Complexity     2578     2582       +4     
============================================
  Files           266      267       +1     
  Lines          8453     8468      +15     
  Branches        997      999       +2     
============================================
+ Hits           6638     6651      +13     
- Misses         1379     1382       +3     
+ Partials        436      435       -1     

Files	Coverage Δ
...g/conversion/InspectitConfigConversionService.java	94.12% <87.50%> (-5.88%)	⬇️
...tit/ocelot/core/config/PropertyNamesValidator.java	75.00% <50.00%> (-3.26%)	⬇️
...fig/conversion/PlaceholderToDurationConverter.java	50.00% <50.00%> (ø)

... and 2 files with indirect coverage changes

[TitusLabs]

Reviewed 11 of 12 files at r1, 4 of 4 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @EddeCCC)