feat(index): support branch name and path aliases

[cmark]

A set of name aliases can be specified for a given, existing branch. This works just like the primary path of the branch and can be used to access the branch. Only a single path alias can exist at a given time which points to a single branch document.

[codecov]

Codecov Report

Patch coverage: 89.04% and project coverage change: +0.03% 🎉

Comparison is base (680f970) 64.08% compared to head (c1e8162) 64.12%.

Additional details and impacted files

@@             Coverage Diff              @@
##                9.x    #1209      +/-   ##
============================================
+ Coverage     64.08%   64.12%   +0.03%     
- Complexity    13137    13158      +21     
============================================
  Files          1799     1799              
  Lines         61537    61594      +57     
  Branches       5690     5696       +6     
============================================
+ Hits          39438    39495      +57     
- Misses        19660    19662       +2     
+ Partials       2439     2437       -2     

Files Changed	Coverage Δ
...nowowl/core/branch/BranchUpdateRequestBuilder.java	81.81% <33.33%> (-18.19%)	⬇️
...national/index/revision/BaseRevisionBranching.java	89.90% <89.58%> (+0.43%)	⬆️
...ional/snowowl/core/branch/BranchUpdateRequest.java	94.11% <91.66%> (+16.33%)	⬆️
...b2international/index/revision/RevisionBranch.java	94.30% <100.00%> (+0.44%)	⬆️

... and 5 files with indirect coverage changes

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