Loki: Handle data source configs with path in the url (#50971)

* loki: fixed param-name

* loki: handle datasource configs with path in the url

* lint fix

pkg/tsdb/loki/api_mock.go

@@ -33,9 +33,13 @@ func (mockedRT *mockedRoundTripper) RoundTrip(req *http.Request) (*http.Response
 }
 
 func makeMockedAPI(statusCode int, contentType string, responseBytes []byte, requestCallback mockRequestCallback) *LokiAPI {
+	return makeMockedAPIWithUrl("http://localhost:9999", statusCode, contentType, responseBytes, requestCallback)
+}
+
+func makeMockedAPIWithUrl(url string, statusCode int, contentType string, responseBytes []byte, requestCallback mockRequestCallback) *LokiAPI {
 	client := http.Client{
 		Transport: &mockedRoundTripper{statusCode: statusCode, contentType: contentType, responseBytes: responseBytes, requestCallback: requestCallback},
 	}
 
-	return newLokiAPI(&client, "http://localhost:9999", log.New("test"), nil)
+	return newLokiAPI(&client, url, log.New("test"), nil)
 }