Add scarb login command to handle registry auth

[DelevoXDG]

Problem

As of after #1570, we're using SCARB_REGISTRY_AUTH_TOKEN to support scarb publish, and potentially other commands that interact with registry and require authentication.

Requiring users to set environment variables doesn't seem like the best UX.

Additionally, this can lead to leaks in bash_history, due to, for example:

export SCARB_REGISTRY_AUTH_TOKEN=scrb_aaaaa

or

SCARB_REGISTRY_AUTH_TOKEN=scrb_aaaaa scarb_build

Proposed Solution

I think it would be great to have an interactive scarb login / scarb auth command that prompts the user to input the auth token, and preferably stores it in some config file.

Notes

No response