Hostname scripts are incompatible with Raspberry Pi OS Bookworm

[cghague]

Related #1668

Our hostname scripts make changes to /etc/hostname directly, which is no longer sufficient nor supported on Raspberry Pi OS Bookworm. We should instead use the hostnamectl tool, or we could call the do_hostname() function in raspi-config.

[mtlynch]

I'd like to go with hostnamectl if possible. raspi-config doesn't seem like they build with the expectation of third-parties depending on them.