Field, Function and test fixes, adding missing struct to node stats

[Jakob3xD]

Description

• Fix FLS role type
• Fix json compare when response is null
• Fix function where the wrong var is given to parse the response
• Add missing node stats cache field

Issues Resolved

Closes #560

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.96%. Comparing base (06a6dc8) to head (11eeb80).
Report is 39 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #572       +/-   ##
===========================================
+ Coverage   57.29%   67.96%   +10.67%     
===========================================
  Files         315      376       +61     
  Lines        9823     8853      -970     
===========================================
+ Hits         5628     6017      +389     
+ Misses       2902     1555     -1347     
+ Partials     1293     1281       -12     

Flag	Coverage Δ
integration	60.39% <100.00%> (+9.55%)	⬆️
unit	15.28% <0.00%> (+2.43%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
opensearchapi/api_indices-mapping.go	95.00% <100.00%> (+1.66%)	⬆️
opensearchapi/api_indices.go	96.07% <100.00%> (+1.16%)	⬆️
opensearchapi/api_nodes-stats.go	100.00% <ø> (ø)
plugins/security/api_actiongroups.go	100.00% <100.00%> (ø)
plugins/security/api_internalusers.go	100.00% <100.00%> (ø)
plugins/security/api_roles-get.go	100.00% <ø> (ø)
plugins/security/api_roles-put.go	84.61% <ø> (ø)
plugins/security/api_roles.go	100.00% <100.00%> (ø)
plugins/security/api_rolesmapping.go	100.00% <100.00%> (ø)
plugins/security/api_tenants.go	100.00% <100.00%> (ø)

... and 265 files with indirect coverage changes

[dblock]

Want to write some tests for this one? Looks like lots of tests failed.

[Jakob3xD]

Want to write some tests for this one? Looks like lots of tests failed.

Test are failing because of the omitempty tag causing the json compare to omit them and resulting in missing fields when comparing. I am currently thinking about a solution.

[Jakob3xD]

I am not totally happy with this solution as I would have liked to not duplicate the structs but there is not lib that compares a struct against a json blob and respects the omitempty tag. Or at least I did not find such a lib.
Therefore duplicating the structs but without omitemtpy is simplest and easiest way of solving this.