Remove GMA specs and update SAML SSO specs

Description of the test

Testcase: gitlab-org/quality/testcases#1756 (closed)

Related issue: #296863 (closed)

This MR:

1. Removes the group managed accounts spec as the feature has been deprecated
2. Renames group_saml_group_managed_accounts_spec => group_saml_enforced_sso_new_account_spec
3. Updates the specs in group_saml_enforced_sso_new_account_spec to test SAML user provisioning
4. Renames group_saml_enforced_sso_spec => group_saml_enforced_sso_git_access_spec

I have created an issue to update the group_saml_enforced_sso_git_access_spec as the current test has become stale after this MR.

How to run the test on local against GDK:

1. Your gitlab.yml file should have the following:

  omniauth:
    enabled: true
    providers:
      - { name: 'group_saml' }

2. Run the test: QA_DEBUG=true CHROME_HEADLESS=false bundle exec bin/qa Test::Instance::All http://localhost:3000 -- --tag orchestrated qa/specs/features/ee/browser_ui/1_manage/group/group_saml_enforced_sso_new_account_spec.rb

Check-list

• Confirm the test has a testcase: tag linking to an existing test case in the test case project.
• Note if the test is intended to run in specific scenarios. If a scenario is new, add a link to the MR that adds the new scenario.
• Follow the end-to-end tests style guide and best practices.
• Use the appropriate RSpec metadata tag(s).
• Ensure that a created resource is removed after test execution.
• [-] Ensure that no transient bugs are hidden accidentally due to the usage of waits and reloads.
• [-] Verify the tags to ensure it runs on the desired test environments.
• [-] If this MR has a dependency on another MR, such as a GitLab QA MR, specify the order in which the MRs should be merged.
• [-] (If applicable) Create a follow-up issue to document the special setup necessary to run the test: ISSUE_LINK