packages,plugins: add package documentation

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/api-docs/api-report.md

@@ -183,6 +183,4 @@ export const ProvidedApisCard: ({ variant }: Props_4) => JSX.Element;
 //
 // @public (undocumented)
 export const ProvidingComponentsCard: ({ variant }: Props_7) => JSX.Element;
-
-// (No @packageDocumentation comment for this package)
 ```

plugins/api-docs/src/index.ts

@@ -14,6 +14,12 @@
  * limitations under the License.
  */
 
+/**
+ * A Backstage plugin that helps represent API entities in the frontend
+ *
+ * @packageDocumentation
+ */
+
 export * from './components';
 export { apiDocsConfigRef } from './config';
 export {