Make Pod health dashboard available to users

What does this MR do?

Add a new out of the box (OOTB) dashboard for monitoring the health of pods in a K8s cluster. It displays CPU, memory, network and disk metrics. The dashboard yaml already exists in Gitlab, but is not visible to users.

This MR:

• Makes the dashboard visible in the dashboard selector on the metrics dashboard page.
• Adds a templating variable to the dashboard yaml. The variable adds a pod selector to the dashboard, which allows users to select which pod's metrics are displayed in the dashboard.
• Sort dashboards alphabetically in the dashboard selector.

Issue: #218649 (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.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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