packages,plugins: add package documentation

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

plugins/kubernetes/api-report.md

@@ -54,6 +54,4 @@ export { kubernetesPlugin as plugin };
 //
 // @public (undocumented)
 export const Router: (_props: Props) => JSX.Element;
-
-// (No @packageDocumentation comment for this package)
 ```

plugins/kubernetes/src/index.ts

@@ -13,6 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
+/**
+ * A Backstage plugin that integrates towards Kubernetes
+ *
+ * @packageDocumentation
+ */
+
 export {
   kubernetesPlugin,
   kubernetesPlugin as plugin,