Redirect Manager: allow creating redirect configurations in a nested hierarchy

[YegorKozlov]

See #3497

The current implementation only allows creating redirect configurations as direct children if the /conf folder, e.g.

 + /conf/my-site/settings/redirects
     - rule1
     - rule2
 + /conf/another-site/settings/redirects
     - rule1
     - rule2

The PR allows creating redirect configurations on any level down, e.g.

 + /conf/level1/settings/redirects
     - rule1
     - rule2
 + /conf/level1/level2/settings/redirects
     - rule1
     - rule2
 + /conf/level1/level2/level3/settings/redirects
     - rule1
     - rule2

[codecov]

Codecov Report

Attention: Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.

Project coverage is 55.81%. Comparing base (ef4f406) to head (604d820).
Report is 53 commits behind head on master.

Files with missing lines	Patch %	Lines
...e/acs/commons/redirects/models/Configurations.java	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3498      +/-   ##
============================================
+ Coverage     55.54%   55.81%   +0.26%     
- Complexity     5582     5622      +40     
============================================
  Files           728      731       +3     
  Lines         29775    29901     +126     
  Branches       3884     3907      +23     
============================================
+ Hits          16540    16689     +149     
+ Misses        11684    11649      -35     
- Partials       1551     1563      +12     

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