Backend: Add checkbox to enable/disable grafana authentication

What does this MR do?

Back End for #33672 (closed)

This MR adds an enabled flag on grafana_integration and allow that flag to be updated and shown via the actions in the projects_settings_operations controller.

This flag will back a checkbox that will allow the user to disable and re-enable embedded Grafana charts.

Screenshots

No front end changes at this time.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• 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

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