Summary:
Add a legocastle job to continuously build the last 10 commits every 4 hours and report lite build binary size to scuba.
Closes https://github.com/facebook/rocksdb/pull/3511
Differential Revision: D7001730
Pulled By: yiwu-arbug
fbshipit-source-id: 7c8ca87c46d663c786a0d32be69ebbe7b19a5eb9
Yi Wu