[OpAMP] fleet-server should request a status report if drift is detected

[michel-laterman]

The opamp spec defines a ServerToAgent.flags.ReportFullState message that a server can use to request that an agent responds with a full status report on the next message.

Fleet-server does not use this ability at the moment.
We should follow the spec and use this flag to get a full status report if the server detects drift.

This should occur if a sequence number is delivered out of order.