WIP: work for prow monitoring

[NymanRobin]

NOTE: This is a draft and is not ready to be merged

It is basically based on the monitoring stack found under kubernetes test-infra monitoring and also the kubernetes-mixins.

The most important part of this if it is to be used as a base for further work is the README.md file which has instructions how to setup kubernetes-mixins locally and can provide a good ground for future work. To be noted the kustomize deployment is not tested the stack has only been tested with helm.

• Figure out how to dynamically generate the mixins and deploy them, while also keeping them up to date.
• Same as above for the prometheus monitoring and alert rules
• Create the kustomize.yaml to mount the dashboards to the grafana pod and the slack webhook as a secret for the alertmanager, also referencing all the components that are needed for the monitoring stack itself
• Figure out the ingress, this pr sets a new endpoint /monitoring but it could be done through a new subdomain as well monitoring.prow.apps.test.metal3.io/ would need to be requested from CNCF

The huge amount of file is since the mixins of prow and kubernetes are generated here, in the other projects it seems it is preferred to dynamically generate these when needed so might be worth to look into

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[NymanRobin]

/hold

[metal3-io-bot]

@NymanRobin: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
markdownlint	aa9b4ba	link	true	/test markdownlint

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