Backup : Handle status update after connection is broken with server

User story:
As a PMM user, I need to get backup status in PMM when the connection between PMM Client and Server disappeared for some period of time.

UI/UX:
N/A

Acceptance criteria

• In case of some backup job is finished during the connection 

Out of scope:

Suggested implementation:

Implement cyclic buffer on PMM agent side with configurable size. (Should be discussed)

How to test:

1. Backup
   1. Start backup
   2. Simulate network disconnect between pmm-client and PMM Server
   3. Wait until backup is finished
   4. Reconnect
   5. Check that backup status is correct in UI