packages,plugins: add package documentation

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

plugins/github-actions/api-report.md

@@ -352,6 +352,4 @@ export type Step = {
   started_at: string;
   completed_at: string;
 };
-
-// (No @packageDocumentation comment for this package)
 ```

plugins/github-actions/src/index.ts

@@ -14,6 +14,12 @@
  * limitations under the License.
  */
 
+/**
+ * A Backstage plugin that integrates towards GitHub Actions
+ *
+ * @packageDocumentation
+ */
+
 export {
   githubActionsPlugin,
   githubActionsPlugin as plugin,