Adding expire option to redis connector

[miki haiat]

Hi ,

We have a use that we need to collect some Meta data window it and group it
by some rules.
Each window can create different set of keys and value ,therefor  the
ability  to set expire could be very helpful .

i started to change the code ,

https://github.com/miko-code/bahir-flink/tree/master/flink-connector-redis/src/main/java/org/apache/flink/streaming/connectors/redis/common

There  is  work to do , but before i continue  if some can review it will
be nice .

thnaks,

Miki