Emit a warning that can be turned off when overwriting built-in .Params values

Fixes #11941

hugolib/params_test.go

@@ -133,6 +133,28 @@ RegularPages: {{ range site.RegularPages }}{{ .Path }}|{{ .RelPermalink }}|{{ .T
 	)
 }
 
+func TestFrontMatterTitleOverrideWarn(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+baseURL = "https://example.org/"
+disableKinds = ["taxonomy", "term"]
+-- content/p1.md --
+---
+title: "My title"
+params:
+  title: "My title from params"
+---
+
+
+`
+
+	b := Test(t, files, TestOptWarn())
+
+	b.AssertLogContains("ARN  Hugo front matter key \"title\" is overridden in params section", "You can suppress this warning")
+}
+
 func TestFrontMatterParamsLangNoCascade(t *testing.T) {
 	t.Parallel()