Support configuring envoy LISTENER_DRAIN_WAIT_TIME_S environment variable

[seanr-cardless]

Is your feature request related to a problem?

The AppMesh Agent provides a LISTENER_DRAIN_WAIT_TIME_S environment variable that can be used to configure how long envoy waits to drain connections.

This currently isn't a property that's configurable through the app-mesh controller. It would be nice if we could configure this drain time so we could properly add enough cleanup time for the other containers to gracefully shutdown in our pod.

Describe the solution you'd like

Allow configuration of LISTENER_DRAIN_WAIT_TIME_S through helm values. A global setting would work.

Describe alternatives you've considered
A description of any alternative solutions or features you've considered.

We're currently constraining our services to gracefully shutdown within the default 20-second envoy drain wait time.