Rename taxonomy kinds from taxonomy to term, taxonomyTerm to taxonomy

And we have taken great measures to limit potential site breakage:

* For `disableKinds` and `outputs` we try to map from old to new values if possible, if not we print an ERROR that can be toggled off if not relevant.
* The layout lookup is mostly compatible with more options for the new `term` kind.

That leaves:

* Where queries in site.Pages using taxonomy/taxonomyTerm Kind values as filter.
* Other places where these kind value are used in the templates (classes etc.)

Fixes #6911
Fixes #7395

hugolib/hugo_smoke_test.go

@@ -27,7 +27,7 @@ func TestHello(t *testing.T) {
 	b := newTestSitesBuilder(t)
 	b.WithConfigFile("toml", `
 baseURL="https://example.org"
-disableKinds = ["taxonomy", "taxonomyTerm", "section", "page"]
+disableKinds = ["term", "taxonomy", "section", "page"]
 `)
 	b.WithContent("p1", `
 ---