Mention badge-default in migration docs, fix typo on popover docs (#23409)

docs/4.0/components/popovers.md

@@ -361,7 +361,7 @@ Updates the position of an element's popover.
     </tr>
     <tr>
       <td>inserted.bs.popover</td>
-      <td>This event is fired after the <code>show.bs.popover</code> event when the tooltip template has been added to the DOM.</td>
+      <td>This event is fired after the <code>show.bs.popover</code> event when the popover template has been added to the DOM.</td>
     </tr>
   </tbody>
 </table>

docs/4.0/migration.md

@@ -188,6 +188,7 @@ The navbar has been entirely rewritten in flexbox with improved support for alig
 - Renamed `.label` to `.badge` to disambiguate from the `<label>` element.
 - Dropped the `.badge` component as it was nearly identical to labels. Use the `.badge-pill` modifier together with the label component instead for that rounded look.
 - Badges are no longer floated automatically in list groups and other components. Utility classes are now required for that.
+- `.badge-default` has been dropped and `.badge-secondary` added to match component modifier classes used elsewhere.
 
 ### Panels, thumbnails, and wells