[ImgBot] Optimize images

*Total -- 46.33kb -> 22.69kb (51.03%)

/docs/high-availability/img/hystrix-semphore-thread-pool.png -- 11.68kb -> 5.11kb (56.27%)
/img/hystrix-semphore-thread-pool.png -- 11.68kb -> 5.11kb (56.27%)
/docs/high-availability/img/hystrix-semphore.png -- 11.49kb -> 6.24kb (45.71%)
/img/hystrix-semphore.png -- 11.49kb -> 6.24kb (45.71%)