Issue Template

Title: Add support for lease/end-time for using endpoints/resources

Description:
When disconnected from the Management Server, envoy would end up using last known information from the Mgmt server. This is probably good for a lot of usecases/deployment, but there are situations where this might actually be harmful for overall system.

Example 1:

For a deployment where Management Server does load balancing and sends the endpoints with weights to the envoys. If a envoy is disconnected from the management server for significant period, it will continue to use the stale weights and endpoints. Although the envoy will route the traffic to endpoints, we might end have

• Some servers move to different ip:port causing less number of endpoints being usable. Which eventually results in server overload.
• Servers getting overloaded as the weights assigned are stale.

Example 2:

SDS information might be stale and should probably be discarded after some time.

Proposal:
This can be address by either having optional lease duration associated with DiscoverResponse sent by management Server.
OR
Add lease specific information to relevant DS.