Add k8s heatmap chart example

What does this MR do?

This adds an heatmap panel type metrics dashboard template, this uses k8s based labels for the query

&4077

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