Merge branch 'docs-add-trivy-db-offline-clarifications' into 'master'

Add clarifications to offline Trivy DB usage

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138758



Merged-by: Russell Dickenson <rdickenson@gitlab.com>
Reviewed-by: Igor Frenkel <ifrenkel@gitlab.com>
Co-authored-by: Igor Frenkel <ifrenkel@gitlab.com>
Co-authored-by: Alexandr Tanayno <atanayno@gitlab.com>