Adapt secure workflow to Product Development Flow

Why is this change being made?

The Secure team is still following a workflow that is slightly different from the Product Development Flow and uses some of the workflow:: labels for a different purpose. This creates confusion and makes it harder to collaborate with all counterparts.

This MR aims at getting closer to the company-wide guideline but still keeps some additions. After experimenting and getting feedback, some of these additions could then be rolled out at the company level.

What changed?

• Secure handbook page (workflow): https://gcs-update-secure-workflow.about.gitlab-review.app/handbook/engineering/development/secure/index.html#workflow

• Secure handbook page (grooming): https://gcs-update-secure-workflow.about.gitlab-review.app/handbook/engineering/development/secure/planning/index.html

Walkthrough video

Using the Issue Board as an Engineering Manager

Using the Issue Board as an Engineer

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what