Add correlations to external URLs in Explore

Correlations is a feature that allows Grafana users to set up links between their data sources. Previously, the link generated would only be from one query to another—meaning results from a query could only generate links to open a second Explore pane with other query results.

With this feature, users can now link to third party web-based software based on their search results. The format follows the standard Grafana format for using variables.