QueryField: Prevent query runs on blur in Explore (#20180)

As discussed in a UX feedback session, it's annoying that queries are
automatically executed in Explore. This change adds props to override
the blur behavior.

- add `onBlur` to Explore query field props
- Explore's query row will pass down an empty function for onBlur to the
query fields
- pass onBlur through to the QueryField component for Loki and
Prometheus
- add test to QueryField to make sure if onBlur is specified, the
onRunQuery is not executed

public/app/plugins/datasource/prometheus/components/PromQueryField.tsx

@@ -297,6 +297,7 @@ class PromQueryField extends React.PureComponent<PromQueryFieldProps, PromQueryF
               query={query.expr}
               onTypeahead={this.onTypeahead}
               onWillApplySuggestion={willApplySuggestion}
+              onBlur={this.props.onBlur}
               onChange={this.onChangeQuery}
               onRunQuery={this.props.onRunQuery}
               placeholder="Enter a PromQL query"