Add the GL Continuous Security Framework page

Why is this change being made?

This MR is the first iteration of the GitLab Security Framework POC.

See https://gitlab.com/gitlab-com/gl-security/security-architecture/general/-/issues/12 for details.

Sub-tasks

• Gather requirements and guidelines from Security teams

Team	DRI	MR	Status
InfraSec	@mlancini	!107064 (closed)	Pending
AppSec	@nmalcolm	!106918 (closed)	Pending
SecResearch	@joernchen	!107356 (merged)	✅ Done
SecAssurance	@jburrows001	!107367 (closed)	Pending

• Add Architecture activity: https://gl-csf.about.gitlab-review.app/handbook/security/gl-csf/architecture.html
• Add template for Architecture description
• Reference the gl-csf CI/CD template

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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