Add JSON Values Schema for Big Bang

In order to help customers understand what values might no longer be valid in 2.0, and aid with future debugging we want to provide a values schema for the umbrella chart.

https://helm.sh/docs/topics/charts/#schema-files

This schema will provide enforcement that customer values are correct prior to deploy, and especially help with the 2.0 transition as some values may no longer be valid.

Our schema should enforce clear restrictions, but still allow the full flexibility for customers to pass in values overrides to charts and other cases where the schema is less well defined.