Add Link to Seismic Shift Whitepaper to /dast/ landing page

What does this MR do?

This MR adds a note box which includes a relevant security resource page to drive traffic and MQLs from docs as discussed in this epic and tracking from this issue. This is the same addition that was made on https://docs.gitlab.com/ee/user/application_security/sast/.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team