Pass log source to the frontend

What does this MR do?

Bubble up the log source used to query log for an environment to the frontend. In turn, this is used:

• to disable the search bar on kubernetes sources (from !21656 (comment 262549742))
• to display a callout encouraging the user to install Elastic Stack on their cluster (from #35604 (comment 242847864) and #122023 (closed))

❗ Enable FF enable_cluster_application_elastic_stack to use this feature.

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.
• 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