Docs: Merge EE doc/user/application_security to CE

What does this MR do?

No EE Port needed, applies cleanly to EE.

This aligns the CE and EE doc/user/application_security docs, as part of the effort to combine docs into a single codebase (&199 (closed)).

This MR:

• Brings in:
  • application_security/container_scanning/index.md
  • application_security/dast/index.md
  • application_security/dependency_scanning/index.md
  • application_security/index.md
  • application_security/license_management/index.md
  • application_security/sast/index.md
  • application_security/security_dashboard/index.md
  • 16 Images related to the above docs.
• No other changes needed, links and badges are fine.

When this MR is merged, the doc/user/application_security docs should hopefully be aligned between CE and EE.

Then, please merge: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/12024, and the issue will be closed.

Related issues

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/61073

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the ~Documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set and that you merge the equivalent EE MR before the CE MR if both exist.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.