Refactor more code in templates (#29236)

Follow #29165. 

* Introduce JSONTemplate to help to render JSON templates
* Introduce JSEscapeSafe for templates. Now only use `{{ ... |
JSEscape}}` instead of `{{ ... | JSEscape | Safe}}`
* Simplify "UserLocationMapURL" useage

modules/templates/helper_test.go

@@ -52,3 +52,7 @@ func TestSubjectBodySeparator(t *testing.T) {
 		"",
 		"Insuficient\n--\nSeparators")
 }
+
+func TestJSEscapeSafe(t *testing.T) {
+	assert.EqualValues(t, `\u0026\u003C\u003E\'\"`, JSEscapeSafe(`&<>'"`))
+}