[feature] Add Sprig to the template processor

[lhriley]

There may be underlying reasons why this wasn't included at some point, but seeing as the Sprig library is pretty well maintained, it would make sense to include it with the kube-gen template processor.

https://github.com/Masterminds/sprig

I think it only requires adding the following here

kube-gen/template_funcs.go

Line 3 in 5534ca5

import (

:

import (
  "github.com/Masterminds/sprig/v3"
  "html/template"
)

and merging these functions here

kube-gen/template_funcs.go

Line 17 in 5534ca5

var Funcs = template.FuncMap{

:

tpl := template.Must(
  template.New("base").Funcs(sprig.FuncMap()).ParseGlob("*.html")
)

[kylemcc]

Not a bad idea! If you're up for it, I'm glad to accept a PR. Otherwise, I can try to have a look this weekend.