Add EKS cluster counts to usage data

What does this MR do?

Adds EKS cluster count to usage data.

Also begins to address a piece of technical debt - when creating provider records in tests, the cluster and provider aren't associated correctly. Correctly setting these attributes caused unrelated failures which required changing the way some clusters are created in tests (particularly when counting collections). These will be fixed properly in #32024 (closed).

Screenshots

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

Performance 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

#22392 (closed)