[Antrea 2.0] Increase the min supported Kubernetes version to v1.19

[luolanzone]

There was a discussion about increasing the minimum supported K8s version to v1.19. #5068 (comment).
This issue for the further discussion and related changes if maintainers come to an agreement about this min version change. As a part of Antrea 2.0 #4832

• add deprecated field for the old API versions
• Documents update

[luolanzone]

Hi @antoninbas @jianjuns @tnqn could you check if we can increase the minimum supported K8s version? not sure we should increase to a higher version or v1.19 is OK. According the K8s release page, the K8s v1.26 will be end of life on 2024-02-28.

[antoninbas]

I feel like increasing it to 1.19 is sufficient, unless we have a good reason to require a more recent K8s version.

For example, I know that the EndpointSlice feature was graduated to GA in K8s v1.23, and the feature gate was removed in K8s v1.25. If we decide that the minimum required version is 1.25, does that enable us to significantly simplify AntreaProxy code?