set request mode
This field indicates how many acknowledgements the servers should receive
before responding to the request. If it is 0 the server will not send any
response (this is the only case where the server will not reply to a
request). If it is 1, the server will wait the data is written to the
local log before sending a response. If it is -1 the server will block
until the message is committed by all in sync replicas before sending a
response. For any number > 1 the server will block waiting for this
number of acknowledgements to occur (but the server will never wait for
more acknowledgements than there are in-sync replicas).