[ImgBot] Optimize images

*Total -- 135.14kb -> 91.77kb (32.09%)

/images/pipeline_task.png -- 46.18kb -> 29.35kb (36.43%)
/images/release_pipeline_task.png -- 88.96kb -> 62.41kb (29.84%)

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

Author: ImgBotApp