[feature] Better support for local & CI workflow for conan remote login

[schwaerz]

What is your suggestion?

Following up on #5443:

It looks like what was implemented back then is no longer available or did not make it into the final Conan 2.x release.

What would be very useful to us (to reduce the required scripting in every repository):

Have one conan remote ... command to

1. Log on in CI using CONAN_LOGIN_USERNAME and CONAN_PASSWORD
2. Log on to the remote when executed locally, where...
   • It shall ask interactively for username and password for a remote if not authenticated
   • It shall not ask for username and passort if already authenticated to the remote - and the authentication token is still valid

Have you read the CONTRIBUTING guide?

• I've read the CONTRIBUTING guide