WebSocket API to report reasons for failure for machine bulk actions

[Peter Makowski]

When machine action performed from the machine page fails, the error message does not report the reason for the failure.

There can be multiple reasons for failure for subsets of machines, I'd suggest that on top of the existing response we add a new key that will allow us to understand the reasons for which each machine failed and making it actionable.

Something along these lines:

"failed_system_ids": [ "abc", "def"],
"failure_details": {
  "failed to perform an action x due to y": [ "abc"],
  "another detailed failure message": ["def"],
}