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

# Documentation request

https://github.com/canonical/cloud-init/commit/143bc9e40f7f33695216db60f73e10a900d1d1cd#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.

Review commit 143bc9e40f7f33695216db60f73e10a900d1d1cd and locate the 24.3 release note. Verify how the nc.openbsd dependency was introduced and document its absence on distributions such as Arch Linux. Done means the release note clearly highlights this breaking dependency.

Written by the indexing model from the issue text.