internal/oauth: cleanup output

- Remove extra newline before message
- Include the token in the URL (instead of requiring the user to manually
  enter it on the website).
- Improve the "call to action"; ENTER can be used to automatically open
  the browser (but the user can manually open it instead), and CTRL-C can
  be used to cancel the login.
- Remove the "Waiting for authentication in the browser…" message, which
  could be confusing if no browser was opened (yet), instead print a message
  after successfully requesting the browser to be opened.

When running `docker login`;

    docker login

    i Info → Using web-based login. To sign in with credentials on the command line, use 'docker login -u <username>'

    Your one-time device confirmation code is: NRJL-BLRL
    Open this URL to authenticate: https://login.docker.com/activate?user_code=NRJL-BLRL

    Press ENTER to open the URL in your browser, or Ctrl+C to cancel.

After pressing `ENTER`, it either prints the "success" message;

    Press ENTER to open the URL in your browser, or Ctrl+C to cancel.

    Opening browser…

or a failure when unable to launch a browser;

    Press ENTER to open the URL in your browser, or Ctrl+C to cancel.

    No browser found. Open the URL above manually to continue.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/reference/commandline/login.md

@@ -183,9 +183,9 @@ $ docker login
 Using web-based login. To sign in with credentials on the command line, use 'docker login -u <username>'
 
 Your one-time device confirmation code is: LNFR-PGCJ
-Press ENTER to open your browser or submit your device code here: https://login.docker.com/activate
+Open this URL to authenticate: https://login.docker.com/activate?user_code=LNFR-PGCJ
 
-Waiting for authentication in the browser…
+Press ENTER to open the URL in your browser, or Ctrl+C to cancel.
 ```
 
 After entering the code in your browser, you are authenticated to Docker Hub