docs: add as property in CFooter api

Author: cesargb

packages/docs/api/footer/CFooter.api.md

@@ -8,6 +8,7 @@ import CFooter from '@coreui/vue/src/components/footer/CFooter'
 
 #### Props
 
-| Prop name    | Description                           | Type   | Values                | Default |
-| ------------ | ------------------------------------- | ------ | --------------------- | ------- |
-| **position** | Place footer in non-static positions. | string | `'fixed'`, `'sticky'` | -       |
+| Prop name    | Description                                                                             | Type   | Values                | Default |
+| ------------ | --------------------------------------------------------------------------------------- | ------ | --------------------- | ------- |
+| **as**       | Component used for the root node. Either a string to use a HTML element or a component. | string | -                     | 'div'   |
+| **position** | Place footer in non-static positions.                                                   | string | `'fixed'`, `'sticky'` | -       |