Fix gateway mock provider

[flomonster]

This PR cleans the x-remote-user-identity and x-remote-user-name when using the mock provider.

Before: mock.identity/Example User
After: mock/mocked

---

I also fixed the username that was not being passed to editoast. As the mock provider was registered as both a session provider and an identity provider, it always matched the identity (which doesn't provide the username).
To solve this problem, I removed the mock provider's identity implementation. By doing so, the require_login field became unused, so I deleted it.

[codecov-commenter]

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Codecov Report

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

Project coverage is 81.42%. Comparing base (997339d) to head (c911486).
Report is 1 commits behind head on dev.

Files with missing lines	Patch %	Lines
gateway/actix_auth/src/providers/mock.rs	0.00%	6 Missing ⚠️
gateway/actix_auth/src/auth_context.rs	0.00%	2 Missing ⚠️
gateway/src/config_parser.rs	0.00%	2 Missing ⚠️
gateway/actix_auth/src/providers/bearer.rs	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #11215   +/-   ##
=======================================
  Coverage   81.42%   81.42%           
=======================================
  Files        1124     1124           
  Lines      113163   113152   -11     
  Branches      758      758           
=======================================
  Hits        92139    92139           
+ Misses      20969    20958   -11     
  Partials       55       55           

Flag	Coverage Δ
editoast	72.47% <ø> (ø)
front	89.96% <ø> (ø)
gateway	2.48% <0.00%> (+0.01%)	⬆️
osrdyne	8.00% <ø> (ø)
railjson_generator	87.58% <ø> (ø)
tests	88.82% <ø> (ø)

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[Khoyo]

Otherwise lgtm

[sim51]

Tested it.
Now I have a mock/mocked (Example User) in my database., so it works!