[Timelion] Communicate the index pattern to the dashboard

[stratoula]

Describe the feature:

We want the timelion visualization to communicate its index patterns to the dashboard in order for the dashboard filters to work. Right now, if I have a dashboard with timelion visualizations that don't use the default index pattern, the filters don't work correctly as they only allow the users to filter by the default index pattern and not the actual index pattern.

Here, I have a timelion vis with a non default index pattern, but this is not communicated to the filters. Filters only display fields from the default one.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[stratoula]

cc @alexwizp