Add the ability to disable shared runners by group - UI

What does this MR do?

This MR adds the ability to disable shared runners on the group level.

UI can be found at Group > Settings > CI/CD > Expand Runner Settings

A user can now disable runners on a group level and subgroups/projects should follow the groups state. A top level group can allow the subgroup to override the top groups setting if the override toggle is set on the top level group.

Check out the screenshots below to get an idea of the state flow while reviewing this MR. 🙇

Screenshots

group	subgroup

group	project

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team