Add health status in issue sidebar for frontend

What does this MR do?

This MR adds health status information to an issue sidebar using GraphQL. The status information is read-only—the next MR will add the ability to edit.

Issue: #36427 (closed)

This feature is behind the feature flag save_issuable_health_status. To turn it on:

bin/rails console
Feature.enable(:save_issuable_health_status)
exit

To edit the health status:

1. Go to your local GraphQL explorer: http://localhost:3000/-/graphql-explorer
2. Copy, paste, amend, then execute the following query to update the health status. Edit the projectPath, iid, and healthStatus values to the ones you want to update.

mutation {
  updateIssue(input: { projectPath: "gitlab-org/gitlab-test", iid: "1", healthStatus: atRisk}) {
    issue{
      iid
      title
      healthStatus
    }
  }
}

Screenshots

Health status	Collapsed sidebar	Expanded sidebar
None
On track
Needs attention
At risk

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