Move AFP Process to it's own repository

So we have: https://agones.dev/site/docs/contribute/agones-feature-proposal/

Which to be fair, not many people take advantage of. This might be for a few reasons - but some of them could be:

1. The AFP process is https://agones.dev/site/docs/contribute/agones-feature-proposal/ - which is nowhere near the contributing guide.
2. If you file an AFP it gets caught up in whole Agones CI -- which is a lot.

So I'm proposing a few things:

1. We move the AFP process folder into its own proposals repository in our org, since it doesn't need much in the way of backing infrastructure.
2. We move the documentation for AFP into the readme for that project
3. We link to it from the contributing guide.
4. We update the Agones site to be replace the AFP proposal to have a "Code Contribution" page that points to the contributing and development guide in the Agones repository.

Thoughts?