Add elastic-stack as gitlab managed app

What does this MR do?

#33782 (closed)

Add a new gitlab-managed app for the elastic stack (Elasticsearch, Fluentbit, Kibana).

This will collect logs from all pods in a cluster and store them in elasticsearch. The logs are then queryable through Kibana

For now the app is behind a feature flag while we work on integrating log collection in the product and writing associated documentation.

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