Add option to allow usage of Helm Templates in all values of `values.yaml` file items about library-charts

[bjw-s]

We already do this for some of our values, for example in the env section. I've been toying with the idea to implementing it in more places but haven't thought through how to best do it.

The main thing we should try to prevent (as always) is jumping the shark with templating. We don't want or need our library to be a generic templating language for a generic templating language for ... etc.

[MurzNN]

Thanks for detailed explanation, yes - yet another templating language will be overkill ;-)
So maybe we can invent some helper function, that simplifies such conversion via single simple line in common.yaml?
Something like:

{{ parseTemplatesInValues envFrom[0].secretRef.name . }}
{{ parseTemplatesInValues persistence.config.existingClaim . }}
{{ include "common.all" . }}