Add includeAncestors to group.milestones graphql

What does this MR do?

Added support for include_ancestors to group milestone GraphQL query. include_descendants is already supported.

Screenshots (strongly suggested)

  group(fullPath: "h5bp") {
    name
    milestones(includeDescendants: true, includeAncestors:true) {
      nodes {
        title
      }
    }
  }

Does this MR meet the acceptance criteria?

Conformity

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• Documentation (if required)
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• 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

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• 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

Related to #323433 (closed)