[ImgBot] Optimize images (#435)

*Total -- 471.48kb -> 357.75kb (24.12%)

/test-screenshots/02-chat-window-opened.png -- 98.43kb -> 74.06kb (24.76%)
/test-screenshots/03-query-typed.png -- 98.37kb -> 74.05kb (24.73%)
/test-screenshots/01-homepage-before-chat.png -- 272.96kb -> 208.21kb (23.72%)
/static/img/autobot-avatar.svg -- 1.71kb -> 1.43kb (16.54%)

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

Author: imgbot[bot]