Add doc about deploying the DHCP daemonset with Multus

[thomasferrandiz]

Also remove doc about customizing the whereabouts image as it can lead to users deploying an image version not compatible with our own chart.

Related issue: rancher/rke2#3917

[manuelbuil]

I'm concerned that the docs become too long and unorganized, which might confuse users, especially if they are not familiar with how Multus works. I think it would be beneficial if we created a new subsection for multus specifying the three IPAM plugins we support:

• host-local
• whereabouts
• dhcp-daemon

For example adding a section: "Multus IPAM options" and then three tabs, as we have with Canal, Cilium and Calico here: https://docs.rke2.io/install/network_options#install-a-cni-plugin.

For host-local, for example.:

host-local IPAM plugin allocates ip addresses out of a set of address ranges. It stores the state locally on the host filesystem, therefore ensuring uniqueness of IP addresses on a single host. Therefore, we don't recommend it for multi-node clusters. This IPAM plugin does not require any extra deployment. For more information: https://www.cni.dev/plugins/current/ipam/host-local/ 

For whereabours, we can use what we already have, which explains what it is and how to deploy it
For dhcp-daemon, we can use what you are providing in this PR

What do you think? I think it helps because then people understand that whereabouts, dhcp-daemon and host-local are alternatives for the same purpose and they don't get overwhelmed by too many multus subsections

[thomasferrandiz]

@manuelbuil good point, I can do that it will be clearer