Add example of docker login with personal access token

What does this MR do?

Adds an example of docker login using a personal access token

Are there points in the code the reviewer needs to double check?

No

Why was this MR needed?

There are no examples in the documentation how to use the personal access token to perform docker login.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

This is a documentation change, most criteria do not apply.

• Changelog entry added, if necessary
• [ X ] Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• [ X ] Squashed related commits together

What are the relevant issue numbers?

None