providers/saml: support authnrequest forceauthn flag

[PeshekDotDev]

Details

Add support for the forceauthn flag in the saml authnrequest. This acts similar to oidc's prompt=login

Closes #8757

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Checklist

• Local tests pass (ak test authentik/)
• The code has been formatted (make lint-fix)

If an API change has been made

• The API schema and clients have been updated (make gen)

If changes to the frontend have been made

• The code has been formatted (make web)

If applicable

• The documentation has been updated
• The documentation has been formatted (make docs)

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.23%. Comparing base (f992754) to head (e177b1e).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
authentik/providers/saml/views/sso.py	40.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22489      +/-   ##
==========================================
- Coverage   93.28%   93.23%   -0.06%     
==========================================
  Files        1032     1032              
  Lines       60059    60084      +25     
  Branches      400      400              
==========================================
- Hits        56029    56020       -9     
- Misses       4030     4064      +34     

Flag	Coverage Δ
conformance	36.60% <18.51%> (-0.01%)	⬇️
e2e	41.84% <33.33%> (-0.03%)	⬇️
integration	32.55% <18.51%> (-0.50%)	⬇️
rust	0.00% <ø> (ø)
unit	92.19% <59.25%> (-0.02%)	⬇️
unit-migrate	92.24% <59.25%> (-0.02%)	⬇️

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