Create a struct with all of Hugo's config options

Primary motivation is documentation, but it will also hopefully simplify the code.

Also,

* Lower case the default output format names; this is in line with the custom ones (map keys) and how
it's treated all the places. This avoids doing `stringds.EqualFold` everywhere.

Closes #10896
Closes #10620

tpl/collections/append_test.go

@@ -18,17 +18,13 @@ import (
 	"testing"
 
 	qt "github.com/frankban/quicktest"
-	"github.com/gohugoio/hugo/config"
-	"github.com/gohugoio/hugo/deps"
-	"github.com/gohugoio/hugo/langs"
 )
 
 // Also see tests in common/collection.
 func TestAppend(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)
-
-	ns := New(&deps.Deps{Language: langs.NewDefaultLanguage(config.New())})
+	ns := newNs()
 
 	for i, test := range []struct {
 		start    any