Security training - update docs for offline environments

Why are we doing this work

Reported in #384506 (closed), our Security Training integration doesn't work in an offline/airgapped environment.

We should update the docs at https://docs.gitlab.com/ee/user/application_security/vulnerabilities/#enable-security-training-for-vulnerabilities with information about this.

Proposal

Add a note:

Note: Security Training utilizes content from a third-party, therefore requiring GitLab to have an internet connection.

Relevant links

Non-functional requirements

  • Documentation:
  • Feature flag:
  • Performance:
  • Testing:

Implementation plan

Verification steps