Reporting: Image Renderer support for panels in streaming LoadingState

### What happened? If users have the feature flag `lokiQuerySplitting` enabled and use Loki data sources in dashboards that are in Reports, it can cause problems when rendering the final PDF (partial renders or missing data). ### What did you expect to happen? The `lokiQuerySplitting` feature flag streams the data and the Image Renderer does not know when the queries ended. The frontend should provide accurately when the rendering of the panels was completed. ### Did this work before? The workaround is to disable the `lokiQuerySplitting` feature flag ### How do we reproduce it? 1. Enable `lokiQuerySplitting` feature flag 2. Create dashboard and panels using a Loki data source 3. Create a Report with said dashboard ### Is the bug inside a dashboard panel? Maybe? ### Environment (with versions)? Grafana: main OS: any Browser: any ### Grafana platform? None ### Datasource(s)? _No response_