Currently, both man pages and gtk-doc HTML documentation are enabled by
the same build option. It is common for users to want to choose whether
to build HTML docs, as not everyone cares about HTML developer docs, but
manpages are intended directly for end-user consumption and should
always be available. At the very least, there should be a separate
option to disable them to avoid accidentally disabling them while trying
to disable HTML developer docs.
Resolves: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/1653