Support the new flow used in Authentik

[mokrinsky]

Authentik introduced the new authentication flow in this PR: goauthentik/authentik#10296. Basically the change is they switched from using type field to just using different component fields for different operations in the flow.

This PR addresses these changes. Now saml2aws works with recent Authentik version (2024.8.3 at a time), but considering I kept tests for previous flow and they still pass, it should work with older Authentik versions as well.

P.S. I'm not that proficient golang developer, so I would appreciate any suggestions, if any.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 29.01%. Comparing base (99d6fe4) to head (3d2422d).
Report is 97 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/provider/authentik/authentik.go	50.00%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1350       +/-   ##
===========================================
- Coverage   42.19%   29.01%   -13.18%     
===========================================
  Files          54       70       +16     
  Lines        6456     9667     +3211     
===========================================
+ Hits         2724     2805       +81     
- Misses       3283     6391     +3108     
- Partials      449      471       +22     

Flag	Coverage Δ
unittests	29.01% <83.33%> (-13.18%)	⬇️

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