Loki: Improve backend instrumentation of CallResource calls (#73899)

* instrument call resource

* capitalize log messages

pkg/tsdb/loki/api.go

@@ -227,8 +227,11 @@ func makeRawRequest(ctx context.Context, lokiDsUrl string, resourcePath string)
 }
 
 func (api *LokiAPI) RawQuery(ctx context.Context, resourcePath string) (RawLokiResponse, error) {
+	api.log.Debug("Sending raw query to loki", "resourcePath", resourcePath)
+	start := time.Now()
 	req, err := makeRawRequest(ctx, api.url, resourcePath)
 	if err != nil {
+		api.log.Error("Failed to prepare request to loki", "err", err, "resourcePath", resourcePath)
 		return RawLokiResponse{}, err
 	}
 
@@ -243,6 +246,8 @@ func (api *LokiAPI) RawQuery(ctx context.Context, resourcePath string) (RawLokiR
 		}
 	}()
 
+	api.log.Debug("Response received from loki", "status", resp.StatusCode, "length", resp.Header.Get("Content-Length"), "took", time.Since(start), "encoding", resp.Header.Get("Content-Encoding"))
+
 	// server errors are handled by the plugin-proxy to hide the error message
 	if resp.StatusCode/100 == 5 {
 		return RawLokiResponse{}, readLokiError(resp.Body)
@@ -256,6 +261,7 @@ func (api *LokiAPI) RawQuery(ctx context.Context, resourcePath string) (RawLokiR
 	// client errors are passed as a json struct to the client
 	if resp.StatusCode/100 != 2 {
 		lokiResponseErr := lokiResponseError{Message: makeLokiError(body).Error()}
+		api.log.Warn("Non 200 HTTP status received from loki", "err", lokiResponseErr.Message, "status", resp.StatusCode, "resourcePath", resourcePath)
 		traceID := tracing.TraceIDFromContext(ctx, false)
 		if traceID != "" {
 			lokiResponseErr.TraceID = traceID