Support nested params when using Pages.GroupByParam

[riskysnail]

What version of Hugo are you using (hugo version)?

$ hugo version
hugo v0.113.0+extended linux/amd64 BuildDate=2024-01-23T04:15:35Z VendorInfo=ubuntu:0.113.0-3ubuntu0.1

Does this issue reproduce with the latest release?

I am not sure

Description

When using Pages.GroupByParam hugo will fail to build if the param used is a nested like the following example.

Frontmatter:

{
   "author": {
       "email": "jsmith@example.org",
       "name": "John Smith"
   },
}

Grouping fails

{{ range .Pages.GroupByParam "author.name" }}

But sorting works

{{ range .Pages.ByParam "author.name" }}

Error

execute of template failed at <.Pages.GroupByParam>: error calling GroupByParam: there is no such a param

I reported this issue on discourse.gohugo.io and was asked to submit this ticket.
https://discourse.gohugo.io/t/how-to-use-groupbyparam-with-param-subkeys/48929

[jmooring]

This behavior is inconsistent with .Pages.ByParam where you can sort by "foo.bar". If we can sort by a dot-chained parameter we should be able to group by it too.

Failing test:

func TestFoo(t *testing.T) {
	t.Parallel()

	files := `
-- hugo.toml --
disableKinds = ['section','rss','sitemap','taxonomy','term']
-- layouts/_default/home.html --
{{- range site.RegularPages.GroupByParam "author.name" -}}
  {{- .Key -}}|
  {{- range .Pages -}}
    {{ .Title -}}|
  {{- end -}}
{{- end }}
-- layouts/_default/single.html --
{{ .Title }}|
-- content/p1.md --
---
title: p1
params:
  author:
    name: John
---
-- content/p2.md --
---
title: p2
params:
  author:
    name: John
---
-- content/p3.md --
---
title: p3
params:
  author:
    name: Will
---
-- content/p4.md --
---
title: p4
---

`

	b := hugolib.Test(t, files)

	b.AssertFileContent("public/index.html", "John|p1|p2|Will|p3|")
}

[github-actions]

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