Docs: improve usage documentation on `launcher.customRuntimeYaml` and environment bootstrapping

[ianpittwood]

Description

Our documentation for the behavior of launcher.customRuntimeYaml in the rstudio-connect chart seems inadequate. The relevant docs.posit.co section explains that this is a one-time read value for the first startup and is ignored afterwards. The values.yaml does mention that this is only used during initialization, but I think it could be reworded for clarity and could include info or links to resources on how to edit environments for a live instance.

I assume it would not be possible at this time, but reading and updating environments from the ConfigMap YAML file on startup could make environment management less confusing and cumbersome in a Kubernetes environment.