Add socket time out environment variable

[mellis13]

This PR adds the socket timeout parameter as a user-configurable option via environment variables. This is important because for commands such as set_model with large models, the internal socket timeout may be exceeded and multiple retries will have no positive affect because more time is needed to complete the action.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.82%. Comparing base (27ac572) to head (86ef2b9).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #474      +/-   ##
===========================================
+ Coverage    78.80%   78.82%   +0.01%     
===========================================
  Files           97       97              
  Lines         7356     7362       +6     
===========================================
+ Hits          5797     5803       +6     
  Misses        1559     1559              

Files	Coverage Δ
include/redisserver.h	60.00% <ø> (ø)
src/cpp/redis.cpp	54.63% <100.00%> (+0.10%)	⬆️
src/cpp/rediscluster.cpp	66.30% <100.00%> (+0.04%)	⬆️
src/cpp/redisserver.cpp	98.96% <100.00%> (+0.04%)	⬆️

[ashao]

Looks good to me. I'm going to put a followup ticket to add the list of SmartRedis configurable parameters to the documentation. They're a bit hard to find at this point and should be surfaced.

Please merge in develop which has the fixes for CI, then this should be good to merge.