[ImgBot] Optimize images

*Total -- 531.77kb -> 432.05kb (18.75%)

/DDIA/r-s-m.png -- 70.82kb -> 40.57kb (42.72%)
/DDIA/data-system.png -- 180.45kb -> 140.33kb (22.23%)
/DDIA/slow-backend.png -- 181.48kb -> 159.36kb (12.19%)
/DDIA/response-times.png -- 99.02kb -> 91.80kb (7.3%)

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

Author: ImgBotApp