feat: add support for /users/merge endpoint

[antonioturdo]

🚨 Proposed changes

Add support for /users/merge endpoint

Resolve #41

⚙️ Types of changes

• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)
• Refactor

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01% 🎉

Comparison is base (228be73) 99.55% compared to head (de9ef2c) 99.57%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #47      +/-   ##
============================================
+ Coverage     99.55%   99.57%   +0.01%     
- Complexity      478      490      +12     
============================================
  Files           135      138       +3     
  Lines           908      931      +23     
============================================
+ Hits            904      927      +23     
  Misses            4        4              

Files Changed	Coverage Δ
src/Endpoint/Users.php	100.00% <100.00%> (ø)
src/Object/Users/MergeIdentifier.php	100.00% <100.00%> (ø)
src/Object/Users/MergeUpdate.php	100.00% <100.00%> (ø)
src/Request/Users/MergeRequest.php	100.00% <100.00%> (ø)

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