gateway: support an username whitelist for OIDC providers

[Khoyo]

Fixes #7229

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 10.87%. Comparing base (bde4844) to head (d17167b).
Report is 7 commits behind head on dev.

Files	Patch %	Lines
gateway/actix_auth/src/providers/oidc.rs	0.00%	9 Missing ⚠️
gateway/src/config_parser.rs	0.00%	2 Missing ⚠️

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Additional details and impacted files

@@              Coverage Diff              @@
##                dev    #7231       +/-   ##
=============================================
- Coverage     28.19%   10.87%   -17.32%     
=============================================
  Files          1128      601      -527     
  Lines        139439   100424    -39015     
  Branches       2804      930     -1874     
=============================================
- Hits          39309    10917    -28392     
+ Misses        98498    88582     -9916     
+ Partials       1632      925      -707     

Flag	Coverage Δ
core	?
editoast	?
front	9.10% <ø> (ø)
gateway	2.43% <0.00%> (-0.02%)	⬇️
railjson_generator	87.49% <ø> (ø)
tests	83.98% <ø> (ø)

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