Explore: Queries the datasource once per run query and uses DataStreamObserver (#17263)

* Refactor: Removes replaceUrl from actions

* Refactor: Moves saveState thunk to epic

* Refactor: Moves thunks to epics

* Wip: removes resulttype and queries once

* Refactor: LiveTailing uses observer in query

* Refactor: Creates epics folder for epics and move back actioncreators

* Tests: Adds tests for epics and reducer

* Fix: Checks for undefined as well

* Refactor: Cleans up previous live tailing implementation

* Chore: merge with master

* Fix: Fixes url issuses and prom graph in Panels

* Refactor: Removes supportsStreaming and adds sockets to DataSourcePluginMeta instead

* Refactor: Changes the way we create TimeSeries

* Refactor: Renames sockets to streaming

* Refactor: Changes the way Explore does incremental updates

* Refactor: Removes unused method

* Refactor: Adds back Loading indication

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

@@ -223,7 +223,7 @@ class PromQueryField extends React.PureComponent<PromQueryFieldProps, PromQueryF
     // Send text change to parent
     const { query, onChange, onRunQuery } = this.props;
     if (onChange) {
-      const nextQuery: PromQuery = { ...query, expr: value };
+      const nextQuery: PromQuery = { ...query, expr: value, context: 'explore' };
       onChange(nextQuery);
 
       if (override && onRunQuery) {