docs(form): Add documentation about FormItemsTemplate and renderers (#1400)

* docs(form): Document Form Renderers

* chore: FormItemsTemplate article polishing

* docs(form): Various refactoring

Author: dimodi

components/form/colums.md renamed to components/form/columns.md

@@ -6,6 +6,7 @@ slug: form-columns
 tags: telerik,blazor,form,edit,form,columns,spacing,column
 published: True
 position: 15
+previous_url: /components/form/colums
 ---
 
 # Form Columns