Create a repository role to grant undici maintainers (but not owners/admin) to triage security vulnerability via GitHub

[mcollina]

Currenlty only admin/owners can triage security vulnerabilities for Undici. I want to create a custom role for that so that other @nodejs/undici members can do the same (maybe with a subteam, undici-security).

[targos]

SGTM

[KhafraDev]

Thank you!

[mcollina]

One week has passed, I'll create it.