[EPIC] Define chart tests for kube-monitoring to be executed

[richardtief]

Context

Currently, the Greenhouse HelmController only checks if the version of a Plugin has been successfully installed/updated. However, no additional checks are made to ensure that the components of the Helm release work as expected.
Using Chart Tests, it is possible to perform a series of tests after a Helm install/upgrade has been executed to check whether the deployed components are working as intended.

Tasks

• [kube-monitoring] Define and implement chart test cases #217

• Enhance PR Workflow with Integration Tests Using Kind Cluster #259

• Add documentation for plugin testing greenhouse#401
  Ref:

• [FEAT] - run ChartTests for a Plugin if test is available greenhouse#106

• [FEAT] - Readiness for Plugin's workload resources greenhouse#185