Guide on How to Upgrade from 1.6.x to 2.0.x

[mpstefan]

As as user of NGF
I want to know how to upgrade to 2.0
So that I can properly use the latest version of NGF.

Acceptance

• New upgrade doc for 1.6 -> 2.0
  • includes upgrade process (fully uninstall NGF including CRDs, install new version)
  • explain that there will be downtime during the upgrade process
  • Users should not have to update or remove their Gateway API CRDs
• Explain what has changed in 2.0
  • architecture
  • new deployment fields in NginxProxy
  • etc
• Links to new features or relevant information