[#4183] manual release changes

https://gitlab.isc.org/isc-projects/kea/-/wikis/Release-Notes/release…

…-notes-3.1.1

[#4066] updated Changelog entry

[#4031] Convert some leftover docs from autotools to meson

[kea-packaging#48] Hammer: Do not reset-failed kea-ctrl-agent because…

… it no longer starts after installation so it no longer fails either

[#3973] release changes