Update READMEs

[sjberman]

Problem: The helm chart README contained a section that is outdated and removed from our official docs. Also, our main README contains some misleading language around supporting a subset of the Gateway API. While we technically do support a subset, the language makes it sound like our intention is to support a subset, which isn't really true and sounds worse than it is.

Solution: Remove the unneeded sections from both READMEs.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

[salonichf5]

why are we removing all information about zero downtime upgrades ( its not outdated? ) - or just trying to specify it in docs ?

[sjberman]

That process isn't relevant anymore after the control/data plane split. Previously, the data plane would be torn down as part of the control plane upgrade. Now, with readiness probes and the separation, the process is smoother.

[salonichf5]

so will we remove this section from officials docs too ?

That process isn't relevant anymore after the control/data plane split. Previously, the data plane would be torn down as part of the control plane upgrade. Now, with readiness probes and the separation, the process is smoother.

[sjberman]

That doc is different, that's focused on upgrading user apps, not nginx/NGF.

[bjee19]

thanks for handling this