[Fleet] Bulk unenroll API doesn't unenroll agents in Elastic Cloud

[kpollich]

To reproduce

1. Create an Elastic Cloud environment
2. Enroll a few agents and stop them
3. Wait for the agents to become inactive
4. Attempt to unenroll them e.g.

POST kbn:/api/fleet/agents/bulk_unenroll
{
  "includeInactive": true,
  "agents": "status:inactive",
  "force": true
}

Observe the agent action is stuck in in progress and never unenrolls the inactive agents.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[kpollich]

Ah I was neglecting to include revoke: true in the API body - including this causes the API to work as expected. We should probably document this as it's a very common procedure.