cmd: add available tests per test category in help

[KaloyanTanev]

Some time ago @gsora spotted that user can run specific tests, however, the user cannot see which tests are available.

Adding the available tests in the help command.
I've added also consts of the different categories.

category: feature
ticket: none

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 56.77%. Comparing base (ddb95fd) to head (3e6f480).

Files	Patch %	Lines
cmd/test.go	90.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3087      +/-   ##
==========================================
+ Coverage   56.73%   56.77%   +0.04%     
==========================================
  Files         208      208              
  Lines       29113    29130      +17     
==========================================
+ Hits        16516    16538      +22     
+ Misses      10751    10746       -5     
  Partials     1846     1846              

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