Use docker token

[fauust]

See: peter-evans/dockerhub-description#10

Not mandatory but good to implement IMO:

1. create a Docker Hub token (needs read/write/delete rights)
2. replace DOCKER_PASSWORD with DOCKER_TOKEN in GH actions secrets.
3. eventually add 2FA authentication on Docker Hub (it was not possible because of that).

[mvdan]

Thanks for this! I actually tried to make DOCKER_PASSWORD into a token in 2020, but then the "update description" action started failing, so we reverted to my actual password: #492 (comment)

More than happy to give this another try. In the process, I'll change the current password and create an entirely new token. I also think that using a different env var name will indeed help to clarify that it's a token and not a password.

As with all these things, we'll do the final test by merging and seeing what happens :)

[mvdan]

Passwords and tokens reset, 2FA enabled, new token created, old password secret deleted, new token secret created. Pulling the trigger; we'll see if anything breaks.

[mvdan]

Looks like it all went well: https://github.com/mvdan/sh/runs/7411624808?check_suite_focus=true

Thanks again for your help!