[Feature Request] Include support for LACP bonds in initramfs

Feature Request:

When installing a system over the network using live installer (subiquity), you can use the kernel cmdline option ip= [1] to provide the network configuration.

In certain situations, it would be ideal to be able to configure a lacp bond during this process. Sometimes the network ports on the switch are configured with lacp bond (802.3ad) and the switch won't let an interface be brought up unless it sends lacpdus.

I've discussed this through a subiquity bug [2] and it was mentioned that there doesn't seem to be any support in our initramfs for LACP bonds [3]. It was requested for a new bug to be filed at the initramfs-tools project for such functionality to get included.

I don't have any use case at the moment, but I've received this request in the past when the customer was still using debian installer. For debian-installer this was once discussed via a debian bug [4] and a patch was proposed [5], but this was never accepted / merged.

Considering that Tte new installer is an _entirely_ different codebase than d-i, the lacp support would have to come from the initramfs.

[1] ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:<dns0-ip>:<dns1-ip>:<ntp0-ip>
[2] https://bugs.launchpad.net/subiquity/+bug/1988480
[3] https://bugs.launchpad.net/subiquity/+bug/1988480/comments/17
[4] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=611250
[5] https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=611250;filename=bonding_v2.patch;msg=39