Improve logs API

What does this MR do?

Extracts some of the changes from !20733 (closed)

• Instead of the logs.json api returning possible pod names next to the logs, a new logs/filters.json is created which returns all filtering information (pods, namespace and ES status) for an environment. This reduces latency before being able to query for logs, and results in better separation of responsibility in the code.
• Instead of the backend defaulting to the first pod of an environment (and first container) when none is requested, move that decision to the frontend, where it will be changed to default to "all pods" in a subsequent MR.

Screenshots

logs view	environments	pods

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