Orchestrator should take info about agents status from backend only

[nulls]

Orchestrator saves AgentStatus using current timestamp, but creates it when creates a heartbeat.

Also, we save AgentStatus twice: when receives a heartbeat and when sends a response on heartbeat

Suggestions:

• store two statuses on AgentStatus: current status and new status
• ~~use timestamp from Heartbeat~~ handled in #1610
• refactor HeartBeatInspector to take information about agents from backend instead of storing it in orchestrator's memory
• ~~AgentStatus has two times, but looks like we set them equally~~

  IIRC, end_time is being updated in the DB until status changes, then the new row is inserted with initially start_time == end_time

[petertrr]

AgentStatus has two times, but looks like we set them equally

IIRC, end_time is being updated in the DB until status changes, then the new row is inserted with initially start_time == end_time

[nulls]

Can close #11