[ImgBot] Optimize images

*Total -- 881.17kb -> 544.05kb (38.26%)

/workshop/.gitbook/assets/guestbook.png -- 160.95kb -> 77.12kb (52.08%)
/workshop/.gitbook/assets/cloudant-docs.png -- 209.38kb -> 113.92kb (45.59%)
/workshop/.gitbook/assets/cloudant-in-resource-list.png -- 181.20kb -> 115.78kb (36.11%)
/workshop/.gitbook/assets/cloudant-url.png -- 329.64kb -> 237.23kb (28.03%)

Signed-off-by: ImgBotApp <[email protected]>

Author: ImgBotApp