[ImgBot] Optimize images

*Total -- 320.10kb -> 212.78kb (33.53%)

/binderhub/static/images/logo_social.png -- 26.27kb -> 10.50kb (60.03%)
/doc/_static/images/favicon.png -- 14.40kb -> 7.44kb (48.35%)
/doc/zero-to-binderhub/private-repo-token.png -- 168.21kb -> 102.22kb (39.23%)
/binderhub/static/images/caretdown-white.svg -- 0.51kb -> 0.36kb (29.94%)
/doc/zero-to-binderhub/ovh/new_project.png -- 31.71kb -> 22.95kb (27.64%)
/doc/zero-to-binderhub/ovh/generate_id_details.png -- 30.86kb -> 24.80kb (19.66%)
/binderhub/static/images/rst-icon.svg -- 4.13kb -> 3.61kb (12.76%)
/binderhub/static/images/markdown-icon.svg -- 4.19kb -> 3.66kb (12.68%)
/binderhub/static/images/logo_square.png -- 11.57kb -> 10.27kb (11.22%)
/binderhub/static/images/clipboard.svg -- 4.33kb -> 4.04kb (6.74%)
/binderhub/static/images/copy-icon-black.svg -- 4.33kb -> 4.05kb (6.56%)
/doc/_static/images/logo.png -- 15.35kb -> 14.67kb (4.42%)
/binderhub/static/images/badge.svg -- 0.93kb -> 0.93kb (0.1%)
/binderhub/static/images/badge_logo.svg -- 3.30kb -> 3.30kb (0.06%)

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