[ImgBot] Optimize images (#1125)

[ImgBot] Optimize images (#1125)

*Total -- 345.51kb -> 231.49kb (33%)

/docs/graph/flow/images/flow6.png -- 51.92kb -> 34.14kb (34.24%)
/docs/graph/flow/images/flow5.png -- 52.29kb -> 34.42kb (34.17%)
/docs/graph/flow/images/flow4.png -- 51.93kb -> 34.24kb (34.06%)
/docs/graph/flow/images/flow8.png -- 38.72kb -> 25.88kb (33.17%)
/docs/graph/flow/images/flow2.png -- 37.81kb -> 25.75kb (31.89%)
/docs/graph/flow/images/flow3.png -- 39.32kb -> 26.79kb (31.87%)
/docs/graph/flow/images/flow1.png -- 36.71kb -> 25.03kb (31.81%)
/docs/graph/flow/images/flow7.png -- 36.81kb -> 25.23kb (31.46%)