Talos 1.14.0 upgrade docs are missing explicit cni: none migration instructions

Current migration docs mention that network configuration is replaced by the node config and flannel configuration documents and neither lists a way to configure cni: none. This can suggest to the reader that cni: none has become the default. The upgrade document further describes that the flannel document can be used to configure flannel, which reinforces the idea that you deploy that document when you want to use flannel and not when you don't. This is incorrect, as flannel is still the default cni and the flannel configuration document is generated by default. The flannel document also does not contain an enabled/disabled field. Instead current cilium and other cni documentation instructs the users to use a patch delete operation in the flannel document to delete the default configuration of flannel. This is - at least for talos configuration so far - an unintuitive method of configuration and I suspect many users will fall for it and accidentally end up with flannel installed.

The document map also does not list the appropriate alternative for cni: none.

Start with the Talos 1.14.0 migration document, the flannel configuration document, the current Cilium and other CNI documentation, and the document map. Document how to configure cni: none, clarify that flannel remains the default and its document is generated by default, and add the appropriate alternative to the document map.