Iterate on social engineering

Why is this change being made?

💡 Provide a detailed answer to the question on why this change is being proposed, in accordance with our value of Transparency.

This MR clarifies that the Red Team may conduct social engineering via phone calls. This was previously excluded from our rules of engagement.

The MR also breaks the "supply chain" techniques into a new line, but there is no actual policy change there.

Social engineering attacks that leverage voice (via phone, video conference, etc) are on the rise. It is important to continue emulating the threats most relevant to GitLab, so we can better practice and prepare our defenses.

Author and Reviewer Checklist

Please verify the check list and ensure to tick them off before the MR is merged.

• 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
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