Fix the dashboard vue app to work with the new and old metrics dashboard routes

Fix the dashboard vue app to work with the new and old metrics and metrics_dashboard routes:

• Do not display error if hasMetrics is false in dashboard.vue. It will be false when no environment exists.
• If the environment_id URL parameter is passed to the metrics dashboard HTML page, add the URL parameter to the metrics_dashboard.json API call, and to the Prometheus proxy API calls.
• this.graphData?.metrics[0].result can sometimes be null, which causes errors on the browser console. Investigate.