[kube-prometheus-stack] Add values schema

[petar-cvit]

Is your feature request related to a problem ?

Hey, could we add the values.schema.json to the kube-prometheus-stack? We are working on a tool rendering UIs for helm charts based on their schema and would love to be able to support this chart as well.

Describe the solution you'd like.

Add the values.schema.json file. In my opinion, it does not have to define all of the available fields but a set of more important fields users would usually update.

Describe alternatives you've considered.

NONE

Additional context.

I would like to take the issue