[ImgBot] Optimize images

*Total -- 5,341.09kb -> 4,073.18kb (23.74%)

/images/kv-availability-and-consistency.png -- 613.10kb -> 446.22kb (27.22%)
/images/twitter-snowflake.png -- 388.45kb -> 283.77kb (26.95%)
/images/doe-kv-store.png -- 1,142.68kb -> 857.99kb (24.91%)
/images/crawler-init.png -- 244.27kb -> 183.76kb (24.77%)
/images/crawler-full.png -- 845.89kb -> 638.22kb (24.55%)
/images/rate-limiter.png -- 427.04kb -> 324.15kb (24.09%)
/images/hash-ring.png -- 290.29kb -> 222.91kb (23.21%)
/images/consistent-hashing.png -- 237.83kb -> 188.57kb (20.71%)
/images/zero-to-million.png -- 1,151.54kb -> 927.60kb (19.45%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp