Add responsibilities of a appsec engineer in Build phase 2

Why is this change being made?

This MR should cover - #10096 (closed)

The following discussion from !69131 (merged) should be addressed:

• @estrike started a discussion: (+3 comments)

  | Collaborators | Product Manager <br/>Software Engineer in Test <br/>Technical Writer <br/>Product Designer <br/> Application Security Engineer|

  The application security stable counterpart would help validate the risk mitigations developed during this phase. This would be done in code review and through the non-blocking application security review process.

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