feat: Add Memcached authentication

[AJIOB]

Must be merged only after #2114 and #2116, because this branch contains changes from both PRs.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 5.71429% with 33 lines in your changes are missing coverage. Please review.

Project coverage is 30.73%. Comparing base (0cc0c62) to head (b5d13f2).
Report is 7 commits behind head on main.

Files	Patch %	Lines
src/config.rs	9.52%	10 Missing and 9 partials ⚠️
src/cache/cache.rs	0.00%	9 Missing ⚠️
src/cache/memcached.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2117      +/-   ##
==========================================
- Coverage   30.91%   30.73%   -0.18%     
==========================================
  Files          53       53              
  Lines       20112    20184      +72     
  Branches     9755     9805      +50     
==========================================
- Hits         6217     6204      -13     
- Misses       7922     7979      +57     
- Partials     5973     6001      +28     

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[AJIOB]

@sylvestre & @Xuanwo, recheck it, please.

I think it is ready to be merged.

[Xuanwo]

Thanks a lot!