[FEATURE] Support multi data source in assistant

[raintygao]

Is your feature request related to a problem?
We will support multi data source in assistant, assistant needs to get the data source selected by other applications from the OSD page and use this data source to connect to the corresponding OS cluster. When the data source selected on the page changes, the assistant should refresh and update accordingly and connect to the new OS cluster.

What solution would you like?

There are two parts that need to be updated.

In OSD, since the data source selector and menu components provided by DSM don't store the selected value after the data source is selected, we will add a service in DSM. After the component is selected, store the selected value after selecting data source and delete the selected value after the component is unmounted. Other plugins such as assistant can get the value through this instance. opensearch-project/OpenSearch-Dashboards#6825

In assistant, we need to integrate the above new service in DSM, and get selected data source through the data source selector in the OSD page on the front end. Meanwhile, the API needs to be upgraded to support passed data source ID and be able to connect to the corresponding OS cluster through specific data source id.

[dblock]

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