[kube-prometheus-stack] add global value to set default image registry

[davgia]

Is your feature request related to a problem ?

I need to configure the chart to use an harbor instance as pull-through cache. I currently need to change each and every component image repository manually.

Describe the solution you'd like.

It would be nice to have something like .Values.global.image.registry that it is used to build the image repositories.

Describe alternatives you've considered.

The alternative is just to go ahead and manually change all image repositories in the chart (for my count there are at least 14)

Additional context.

No response

[davgia]

I am asking for something like this: main...davgia:helm-charts:feature/base-image-registry