On new deployments, prompt user for username and password on the frontend #1763

Problem Summary

When you install Coder for the first time, users must install & use the CLI to set up their user account with the following command coder login <url>. If they visit the web dashboard directly, they will be faced with a login screen and no way to set up their account.

If you are an admin you need an account to get started with (user #1). We need something similar to a "Welcome to coder, set up your first account" when you first deploy. This is only for the admin.

Are there any workarounds to get this functionality today?

Running coder login [url] on the CLI, then using the terminal

Definition of Done

For a complete frontend experience, Coder can prompt the admin when they first visit the access URL to set the first user's email, username, and password, just as they would for coder login

Notes

The API for this is available now.

1. Design and build the registration page.
2. Figure out if you need to show the registration page and show it.
   This issue may need to be broken up into those 2 pieces above.