Add API token env var as login option for Clever Tools

[davlgd]

As API tokens are close to be available, we should allow users to use them as login option for CLI, as we do for CLEVER_SECRET and CLEVER_TOKEN we could manage a CLEVER_API_TOKEN.

If used:

• Requests to the API are sent with CLEVER_API_TOKEN as bearer token
• User can use any command, but not login, logout, tokens