feat: Add outputList template function

[halostatue]

Resolves #4253

[halostatue]

This is mostly a proof of concept, but if the limitations list … | toStrings is acceptable, then I think we're OK. Otherwise, we'll need to essentially implement toStrings internally to outputList.

I’m also not particularly fond of the name. However, I have been able to run the template in #4253 successfully:

$ go run . execute-template \
  '{{- $opts := dict
        "show-help" true
        "ordered" true
        "no-limit" true
        "header" "Choose a movie poison"
        "options" (list "cyanide" "arsenic" "iocaine powder") 
  -}}{{ includeTemplate "multichoice.tmpl" $opts }}'
["arsenic","iocaine powder"]

[twpayne]

Looks good, and I think this feature is necessary -- as you say, there's no way to pass a variable number of arguments to a Go template function.

[halostatue]

I’m going to merge this so it's in the next release. It works and I was able to get it working with gum using that template, so all is good.

I think that this is useful, but think it might be better to incorporate my "multichoice" template as a feature suggested in #4252 (since I want to be able to use it for init, I would rather not have to ensure that gum is installed to init a repo).