[MDS] Update Data source selector behavior for defaultOption (#6372)

* Refactor selector component changes

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

* Refactor selector

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

* Add unit tests for selector component

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

* Set initial state as [] to prevent page breaking

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

* Remove change

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

* Add changelog

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

* Update snapshots

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

* Update snapshots and fix tests

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

* Fix merge conflict

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

---------

Signed-off-by: Huy Nguyen <73027756+huyaboo@users.noreply.github.com>
Co-authored-by: Lu Yu <nluyu@amazon.com>

CHANGELOG.md

@@ -85,6 +85,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - [Multiple Datasource] Add default icon in multi-selectable picker ([#6357](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/6357))
 - [Workspace] Add APIs to support plugin state in request ([#6303](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/6303))
 - [Workspace] Filter left nav menu items according to the current workspace ([#6234](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/6234))
+- [Multiple Datasource] Refactor data source selector component to include placeholder and add tests ([#6372](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/6372))
 
 ### 🐛 Bug Fixes