[Multiple Datasource] Data source multi selectable component should return the selected data sources and return to the callback function after initial load

[BionIT]

Is your feature request related to a problem? Please describe.
Currently, search relevance plugin and query workbench plugin would use the multi selectable component as a filter, and by requirements, the multi selectable will select all data sources by default, however the selected data sources are not passed to callback function until there is a change event.

Describe the solution you'd like
Multi selectable component should pass selected data sources on the initial load to the call back function

Describe alternatives you've considered
Instead of select all options, do not select any options as the default state, then that means user need to always make a selection first

Additional context

Add any other context or screenshots about the feature request here.

[huyaboo]

Taking a look

[BionIT]

Thanks @huyaboo!