PMM become broken and very hard to recover (backup only ) in case of deleting pmm-server node and pmm-agent from it
Now we let users remove pmm-server node via API and because of this we might not be able to monitor remote services.
We shouldn't let user remove pmm-server node via API.
Suggested error/output message: "Invalid operation: Removing pmm-server node prevents remote monitoring"
First part can be omitted or changed if there is a prevailing convention for other messages.