For grafana monitor, fixes bug with invalid tenant ID

[thunef]

There was an issue with Grafana synthetic monitoring which resulted in these errors:

{"level":"error","ts":1704550886.2006788,"logger":"gcloud-monitor","msg":"Failed to update monitor","error":"check update request: status=\"400 Bad Request\", msg=\"Invalid tenantId for user\", err=\"bad request\"","stacktrace":"github.com/stakater/IngressMonitorController/v2/pkg/monitors/grafana.(*GrafanaMonitorService).Update\n\t/workspace/pkg/monitors/grafana/grafana-monitor.go:146\ngithub.com/stakater/IngressMonitorController/v2/pkg/monitors.(*MonitorServiceProxy).Update\n\t/workspace/pkg/monitors/monitor-proxy.go:101\ngithub.com/stakater/IngressMonitorController/v2/pkg/controllers.(*EndpointMonitorReconciler).handleUpdate\n\t/workspace/pkg/controllers/endpointmonitor_updated.go:26\ngithub.com/stakater/IngressMonitorController/v2/pkg/controllers.

The reason was that tenant was picked from config when it should be picked from the actual check

[github-actions]

@thunef Image is available for testing. docker pull stakater/ingressmonitorcontroller:SNAPSHOT-PR-567-2ae20043