plugins: refactory to use default export for new backend system

Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Co-authored-by: Camila Belo <camilaibs@gmail.com>
Co-authored-by: Johan Haals <johan.haals@gmail.com>
Co-authored-by: Philipp Hugenroth <philipph@spotify.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/techdocs-backend/alpha-api-report.md

@@ -6,7 +6,8 @@
 import { BackendFeature } from '@backstage/backend-plugin-api';
 
 // @alpha
-export const techdocsPlugin: () => BackendFeature;
+const techdocsPlugin: () => BackendFeature;
+export default techdocsPlugin;
 
 // (No @packageDocumentation comment for this package)
 ```

plugins/techdocs-backend/src/alpha.ts

@@ -13,4 +13,5 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-export { techdocsPlugin } from './plugin';
+
+export { techdocsPlugin as default } from './plugin';