[FEATURE] Enabling remote index support

[amitgalitz]

Is your feature request related to a problem?
We currently don't support remote index selection from the AD Dashboards as those indices don't show up in the index dropdown box and also if a user includes any index with ":" manually we block the ability to show any timestamp, data filter or feature selection.

What solution would you like?

• We should implement a similar solution to Alerting Dashboards where we allow users to select additional remote clusters and then display the indices and aliases from each of these clusters.
• Users should be able to select any number of remote indices and local indices, and be able to select a timestamp from those indices along with setting a data filter with the simple filter selector. We should also be able to display fields from remote indices when selecting features and categorical fields.