Add Community Moderator for FIL RetroPGF - Onkar

[Onkar-san]

Summary
Onkar-san's permissions are temporary to enable self-service moderation of filecoin-project/community#744.

They need write permissions per https://docs.github.com/en/communities/moderating-comments-and-conversations/managing-disruptive-comments.

This can be removed 2025-12-01. (1st December)

[BigLep]

This was handled with #166 . We can resolve 2025-12-01 when it's reverted.