Loki: add backend-forward mode to queries, update log-row-context (#47726)

* loki: add helper function to sort dataframe by time

* loki: add direction-attribute to queries

* loki: make log-row-context code backward-compatible

* better comment

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

* fixed test

* simplified code

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

pkg/tsdb/loki/api.go

@@ -29,6 +29,8 @@ func makeRequest(ctx context.Context, lokiDsUrl string, query lokiQuery) (*http.
 	qs := url.Values{}
 	qs.Set("query", query.Expr)
 
+	qs.Set("direction", string(query.Direction))
+
 	// MaxLines defaults to zero when not received,
 	// and Loki does not like limit=0, even when it is not needed
 	// (for example for metric queries), so we