Add "IESG" group at top of Groups menu

[JayDaley]

Description

Currently there is no menu link to the IESG group. Best above the "By area/parent" menu divider.

Code of Conduct

• I agree to follow the IETF's Code of Conduct

[Spectre17]

Where should that link go to? https://datatracker.ietf.org/area/?

[rjsparks]

https://datatracker.ietf.org/group/iesg/about/

[Spectre17]

Done. Let me complete a commit on that shortly.