Improve error message if the user is not logged in

[djs55]

- What I did

Improved the error message when not logged in. The main problem is that the suggestion to "use the Docker Login command" will not work easily if

• 2FA is required
• SSO is being enforced (so no old password logins allowed)

An advanced user can figure this out by using a PAT, but the simplest thing for most users is to log in via the Docker Desktop UI which will handle the 2FA/SSO for you transparently.

- How I did it

I listed the options in the message, leaving the simplest one for new users at the end.

- How to verify it

Before if you docker logout:

> .\docker-scan.exe scan alpine:latest
failed to get DockerScanID: You need to be logged in to Docker Hub to use scan feature.
please login to Docker Hub using the Docker Login command

After this change if you docker logout :

> .\docker-scan.exe scan alpine:latest
failed to get DockerScanID: You need to be logged in to Docker Hub to use the scan feature.

If you are not using Docker Desktop, either
- use the "docker login" CLI command with a username and password. Note this will not work if
  2FA is required or if SSO enforcement is enabled on Docker Hub; or
- use the "docker login" CLI command with a username and Personal Access Token. This requires
  a token to be generated in advance.

If you are using Docker Desktop: login via the UI or whale menu

- Description for the changelog

• Improve the error message if you are currently logged out.

- A picture of a cute animal (not mandatory)