[kube-prometheus-stack] Propagate global.imageRegistry to operator-managed prometheus images

[omeryahud]

What this PR does / why we need it

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes [kube-prometheus-stack] global.ImageRegistry does not affect prometheus image for all instances #4734

Special notes for your reviewer

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [prometheus-couchdb-exporter])

[omeryahud]

@jkroepke Would appreciate your review, thanks!

[jkroepke]

Could you please explain, why this PR solves #4734?

[omeryahud]

Could you please explain, why this PR solves #4734?

Looking at the prometheus-operator deployment, I saw that if .Values.prometheusOperator.prometheusDefaultBaseImage is not provided, .Values.global.imageRegistry is completely ignored.
I also noticed this is the same for all other images, however, all other images had their default in the values file, so I decided to simply align the prometheus image to the rest.

helm-charts/charts/kube-prometheus-stack/templates/prometheus-operator/deployment.yaml

Lines 90 to 92 in 1e4b812

	{{- if .Values.prometheusOperator.prometheusDefaultBaseImage }}
	- --prometheus-default-base-image={{ .Values.global.imageRegistry | default .Values.prometheusOperator.prometheusDefaultBaseImageRegistry }}/{{ .Values.prometheusOperator.prometheusDefaultBaseImage }}
	{{- end }}

[omeryahud]

Looking at it again, maybe the alert-manager image can receive the same treatment.
If this solution is acceptable, let me know and I'll open a separate PR for it as well