[Multiple Datasource] Pass selected data sources to plugin consumers …

…when the multi-select component initially loads (#6333)

* Add callback function to initial load

Signed-off-by: Huy Nguyen <73027756+huyaboo@users.noreply.github.com>

* Add to CHANGELOG

Signed-off-by: Huy Nguyen <73027756+huyaboo@users.noreply.github.com>

---------

Signed-off-by: Huy Nguyen <73027756+huyaboo@users.noreply.github.com>
(cherry picked from commit cb24346)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

# Conflicts:
#	CHANGELOG.md

src/plugins/data_source_management/public/components/data_source_multi_selectable/data_source_multi_selectable.tsx

@@ -70,6 +70,10 @@ export class DataSourceMultiSelectable extends React.Component<
             ...this.state,
             selectedOptions,
           });
+
+          this.props.onSelectedDataSources(
+            selectedOptions.filter((option) => option.checked === 'on')
+          );
         }
       })
       .catch(() => {