Remove enable_cluster_application_crossplane FF

What does this MR do?

Removes enable_cluster_application_crossplane feature flag. The app should now appear by default in the application list (see screenshot below)

Related issue: #36714 (closed)

Screenshots

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.