[llvm] [Docs] Update Maintainer in Developer Policy (PR #154687)

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

Thanks for working on this, but we'll need this to go through the usual RFC process too. Can you post an RFC to Discourse and then link that post with this PR?

https://github.com/llvm/llvm-project/pull/154687