Starts one run of every plan in the group, exactly as POST /v1/simulation/plan/{planId}/job would for each, and groups the runs into a run group whose combined report is announced through the group's notification settings once it is ready. This places real calls. Config-managed groups can be run here too.

Returns the run group. Poll GET /v1/simulation/run-group/{groupId} until latestReport.status is READY.

If a plan cannot start after others did, the runs that started are still grouped and the 400 names the run group id.