Update the Learning pathway / GTN

[scorreard]

• Add Labs engine as "choose your own training" to the lab creation tutorial + australian paper to the GTN --> Tag Gareth for review
• Inform users that they can host a lab in a git repo that is not codex
• Mention that each codex/lab must be attached to a community
  A lab should not be project-bound in the codex. If it's project bound, you can host it somewhere else (local GitLab for example).

[paulzierep]

galaxyproject/training-material#6963

[scorreard]

Did a follow up PR to include the Lab Engine as a "choose your own adventure"
galaxyproject/training-material#6972