add a new mode for graceful termination with the new server run option
'shutdown-send-retry-after'
- shutdown-send-retry-after=true: we initiate shutdown of the
HTTP Server when all in-flight request(s) have been drained. during
this window all incoming requests are rejected with status code
429 and the following response headers:
- 'Retry-After: N' - client should retry after N seconds
- 'Connection: close' - tear down the TCP connection
- shutdown-send-retry-after=false: we initiate shutdown of the
HTTP Server as soon as shutdown-delay-duration has elapsed. This
is in keeping with the current behavior.
Kubernetes-commit: 3182b69e970bd1fd036ff839fdf811f14e790244