[docs]: new dependency on nc.openbsd should be emphasized in the 24.3 release note

[AkihiroSuda]

Documentation request

143bc9e#diff-eb94d50ed1a0a76032438b4bc5bccb389e9cc03d6766d7881463d8ee75f21f8fR25 introduced the dependency on nc.openbsd, but this binary is missing by default on several distros such as ArchLinux (https://gitlab.archlinux.org/archlinux/packaging/packages/cloud-init/-/issues/3).

This is a huge breaking change and should be emphasized in the 24.3 release note.

[TheRealFalcon]

Thanks @AkihiroSuda , we'll update the docs noting this along with python-based solution for those that don't have netcat.

[dvzrv]

Maintaining cloud-init for Arch Linux, I have also found the documentation for the 24.3 release to be lacking (also see #5489 (comment)).
This led to a broken cloud-init package, but also a broken installation medium for the distribution.

It would be great to circumvent these types of issues in the future by clearly stating what is the exact breaking change. 🙏
Also, relying on openbsd-netcat should be re-evaluated, if it can indeed just be replaced by a simple Python script (see #5489 (comment)).
The new dependency comes with issues for some downstreams (such as Arch Linux) and is not really a super well-maintained upstream in my eyes.

To be more specific:
While we do have openbsd-netcat, its feature-set is in part depending on Debian patches (which probably could now be considered "the" upstream) and is not compatible with gnu-netcat.
Arch Linux does not have an alternatives system, so openbsd-netcat and gnu-netcat can not be installed side-by-side.