cli: Add password option

In add-forge-now pipeline this option will be useful to generate token if the former one has expired. I tried to pass the password from stdin but the password prompt is still displayed:

swh@swh-toolbox-7f8bdcbb84-x9n84:~$ echo $PASSWORD | swh auth --oidc-server-url https://auth.softwareheritage.org/auth/ --realm-name SoftwareHeritageStaging generate-token gsamson
Password:

Related to swh/infra/sysadm-environment#5025 (closed)