[ImgBot] Optimize images (#3321)

*Total -- 1,740.68kb -> 1,353.03kb (22.27%)

/Website/docs/img/system-wide-policy-indicator.png -- 53.51kb -> 28.15kb (47.4%)
/Website/static/img/preview-tabs-drag-drop.gif -- 1,687.17kb -> 1,324.89kb (21.47%)

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

Author: imgbot[bot]