[llvm] [Github] Add renovate configuration for Github Actions (PR #159899)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> It looks like you need to file your own PR for that, as renovate-bot is overwriting this one.

Yeah, not sure why it's doing that. We need to merge this PR though in order to enable it. I've manually updated everything for now with the config that I've confirmed as working and will keep an eye on things to make sure nothing goes haywire.

https://github.com/llvm/llvm-project/pull/159899