[ImgBot] optimizes images (#17741)

*Total -- 171.97kb -> 127.26kb (26%)

/swarm/api/testdata/test0/img/logo.png -- 17.71kb -> 4.02kb (77.29%)
/cmd/clef/sign_flow.png -- 35.54kb -> 20.27kb (42.98%)
/cmd/clef/docs/qubes/qrexec-example.png -- 18.66kb -> 15.79kb (15.4%)
/cmd/clef/docs/qubes/clef_qubes_http.png -- 13.97kb -> 11.95kb (14.44%)
/cmd/clef/docs/qubes/clef_qubes_qrexec.png -- 19.79kb -> 17.03kb (13.91%)
/cmd/clef/docs/qubes/qubes_newaccount-2.png -- 41.75kb -> 36.38kb (12.86%)
/cmd/clef/docs/qubes/qubes_newaccount-1.png -- 24.55kb -> 21.82kb (11.11%)