Resolve "[FE] Create setting to force the user to register/use new credentials for a specific group"

What does this MR do?

Improve SAML settings with validation, design, and help text

• SAML settings checkboxes now use toggle buttons
• Client-side validation for enabling/disabling various SAML options
• Helper text and callouts depending on which options are enabled

(In all honesty, it might've been faster to move this section into Vue 😆)

Screenshots

Before

After

SAML disabled	SAML enabled	Enforce SSO enabled	Group managed accounts enabled

Demo

10206-demo

How to test

You need to add the below to your config/gitlab.yml file

providers:
  - { name: 'group_saml' }

Enable the following feature flags in the Rails console (rails c):

• Feature.enable(:enforced_sso)
• Feature.enable(:group_scim)
• Feature.enable(:group_managed_accounts)

Then select a group -> hover settings -> select SAML SSO

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/10206

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• ~~Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.~~
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer

Closes #10206 (closed)