Feature/show memory cpu on cluster list

What does this MR do?

frontend : Implemenentation for #207031 (closed)

backend : Does a simple hotfix to guarantee that we return nodes: nil instead of nodes: [] whenever we fail to load nodes data, as the FE understands [] as zero nodes and would stop the polling.

Disclaimer

Why I created the k8sQuantityToGb and k8sQuantityToCpu functions?

Kubernetes has this concept of Quantities. It’s basically a golang object that adds SI unit suffixes to whole numbers to represent fractual numbers instead of using floating numbers. E.g.: 10.5 is represented as 10500m (milli). Other SI suffixes could be returned like: Ki (kibibytes), (Mi) and n(nano).

From our tests on the Kubernetes metrics API. Usually CPU allocatable capacity is in (m) milli-cores. CPU usage is usually (m) mili-cores or (n) nano-cores. Memory allocatable capacity is in (Ki) kibibytes as well as memory usage.

Screenshots

On GDK:

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