Document supported CNI versions

[dilyanpalauzov]

The CNI interface specification has several versions: 1.0.0, 0.4.0, 0.3.1. Please write down which cniVersion of the specification is supported.

Note that the cni-plugins (implementing the cni specification) are currently at version 1.1.1 and the plugins may implement at the same time several cni-specification versions.

The file https://github.com/containers/podman/blob/main/cni/87-podman-bridge.conflist contains "cniVersion": "0.4.0", but I guess this is outdated.