packages,plugins: add package documentation

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

packages/search-common/api-report.md

@@ -81,6 +81,4 @@ export interface SearchResultSet {
   // (undocumented)
   results: SearchResult[];
 }
-
-// (No @packageDocumentation comment for this package)
 ```

packages/search-common/src/index.ts

@@ -13,4 +13,11 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
+/**
+ * Common functionalities for Search, to be shared between various search-enabled plugins
+ *
+ * @packageDocumentation
+ */
+
 export * from './types';