Prometheus workload loader

[LeaveMyYard]

• Implemented ability to select an alternative workload loader
• Implemented Prometheus workload loader
• Refactored Kube API workload loader: moved separate logic (for each Kind) to a separate class
• List clusters on centralized prometheus
• Scanning multiple clusters in prometheus mode?
• Test running from robusta UI
• Test prometheus mode on centralized prometheus
• A lot of testing
• Fix tests (mocks are now broken)

Testing issues found:

• For some reason auto-discovery does not work
• Prometheus mode does not gather HPA data
• Something is now broken with HPAKey

[deutschj]

When testing using the prometheus mode on a centralized Prometheus (VictoriaMetrics), I encountered the following errors.
I specified the labels --prometheus-label and --prometheus-cluster-label according to the docs:

python krr.py simple -p https://vmauth.xxx.com --prometheus-auth-header "<redacted>" --prometheus-label cluster -l k8s0-q --mode prometheus

To me it seems that the query includes the wrong label here, and should be avg by(cluster) instead of using the cluster name.