Convert SAML module to class

What does this MR do?

Convert SAML module to class.

When running the test locally, the following failures were detected.

bundle exec spring rspec -- ee/spec/features/groups/saml_providers_spec.rb

<SNIP>

Failure/Error: return yield unless new(admin).admin_mode?                                                                           
                                                                                                                                              
TypeError:                                                                                                                          
wrong argument type Class (expected Module)                                                                                       
# ./ee/app/services/group_saml/saml_provider/update_service.rb:6:in `include'                                                       
# ./ee/app/services/group_saml/saml_provider/update_service.rb:6:in `<class:UpdateService>'                                         
# ./ee/app/services/group_saml/saml_provider/update_service.rb:5:in `<module:SamlProvider>'                                         
# ./ee/app/services/group_saml/saml_provider/update_service.rb:4:in `<module:GroupSaml>'                                            
# ./ee/app/services/group_saml/saml_provider/update_service.rb:3:in `<main>'  

The BaseService module also has an initialize method which signals this should have been a class instead.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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• I have self-reviewed this MR per code review guidelines.
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Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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