Many commits squashed into one after I fought the danger-bot for more
time than I care to admin.

Add high-level steps of airgap

Add a link on Secure page & flesh out offline page more

Fix some markdown lint errors

Remove license scanning placeholder

Revert unintentional package change

Apply suggestion to
 doc/user/application_security/offline_deployments/index.md

Apply suggestion to
 doc/user/application_security/offline_deployments/index.md

Apply suggestion to
 doc/user/application_security/offline_deployments/index.md

Update text to mention package repos

Add SAST link

Address feedback given during the review

Add DAST link

Remove dependency scanning link until its merged