Add query options to backend datasource plugin

[ashritha-singu]

Hi, Can I get more information on how to implement query options with variable type "Query" in the backend data source plugin using Go. I am having trouble finding the documentation. I got the other variable types working using applyTemplateVariables but couldn't get much information on implementing metricFindQuery function.
Right now when I select my plugin under data source, the query field is not populating. Only the regex field shows up.