Improve/clarify migration documentation

[perolausson]

What would you like to be added:

Can you please review the documentation under

https://gateway-api.sigs.k8s.io/guides/getting-started/migrating-from-ingress-nginx/#lots-in-progress

As it seems to imply some future work which I believe is now completed?

If you still want to write forward statements in documentation (no reason why not to) then please include the year for whatever tentative dates you have in mind so that one can avoid wondering if something is going to or has already happened.

Why this is needed:

While going through migration documentation I noticed that there are forward statements that seem to now be obsolete.

[Stevenjin8]

@perolausson we've been heads down working on approving more annotation support, but thanks for the heads up. I'll update the blog. We are trying to get a release before the retirement of Ingress NGINX. I recognize that this timeline isn't ideal and I would like to release something usable as soon as possible, but we're working with tight deadlines here.