chore: support graceful shutdown

[appleboy]

// ChangeMaxInFlight sets a new maximum number of messages this comsumer instance
// will allow in-flight, and updates all existing connections as appropriate.
//
// For example, ChangeMaxInFlight(0) would pause message flow
//
// If already connected, it updates the reader RDY state for each connection.

1. Change MaxInFlight
2. wait for stop channel

Signed-off-by: Bo-Yi Wu [email protected]