feat: add saml group links

[abhiandthetruth]

CLOSES #2270

[nejch]

Just ping us here if you get stuck with anything @abhiandthetruth. Thanks for working on this!

[abhiandthetruth]

@nejch occupied with some other work atm. Will try to complete soon

[codecov-commenter]

Codecov Report

Merging #2367 (3405a25) into main (9d2b1ad) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2367   +/-   ##
=======================================
  Coverage   95.96%   95.97%           
=======================================
  Files          80       80           
  Lines        5331     5342   +11     
=======================================
+ Hits         5116     5127   +11     
  Misses        215      215           

Flag	Coverage Δ
api_func_v4	83.73% <90.90%> (+0.03%)	⬆️
cli_func_v4	82.38% <90.90%> (+0.01%)	⬆️
unit	87.75% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
gitlab/v4/objects/groups.py	90.55% <100.00%> (+0.61%)	⬆️

[abhiandthetruth]

@nejch can you have a look?
Disabled functional tests since cant get them to work, getting 401 while creating a new saml group link. Might need to setup an identity provider in CI.

[nejch]

@nejch can you have a look? Disabled functional tests since cant get them to work, getting 401 while creating a new saml group link. Might need to setup an identity provider in CI.

note to self:

# https://docs.gitlab.com/ee/integration/omniauth.html#configure-initial-settings
# https://docs.gitlab.com/ee/integration/saml.html#general-setup
gitlab_rails['omniauth_allow_single_sign_on'] = ['saml']
gitlab_rails['omniauth_block_auto_created_users'] = false
gitlab_rails['omniauth_providers'] = [
  {
    name: "saml",
    args: {
      assertion_consumer_service_url: "http://localhost:8080/users/auth/saml/callback",
      idp_cert_fingerprint: "43:51:43:a1:b5:fc:8b:b7:0a:3a:a9:b1:0f:66:73:a8",
      idp_sso_target_url: "https://login.example.com/idp",
      issuer: "http://localhost:8080",
      name_identifier_format: "urn:oasis:names:tc:SAML:2.0:nameid-format:persistent"
    }
  }
]

[nejch]

Thanks for the work here @abhiandthetruth! The request body matcher in the unit tests will really help with confidence until we have a functional test setup for this.

I've squashed the commits here as the others weren't strictly for the changelog as a feat :)