Support browser login workflow

[jooola]

TL;DR

Allow to setup a context with a token using a browser.

Expected behavior

• In the CLI, initiate the creation of a new context
• Either prompt for the desired authentication flow (manual, or browser) or read it from a flag
• Open a browser for the user to authenticate in console.hetzner.com, or directly jump to next step if already authenticated (should we ask confirmation about the current account?)
• Select the project for which we should setup a new token
• Configure the new token name and permissions, (ideally also set an expiration date)
• Create the new token in the console and save the token in a CLI context

[WolfgangFahl]

nextcloud has such a workflow and it is quite intuitive