mkosi: use the new mkosi.conf suffix

Mkosi 14 is out, compat with old mkosi is not terribly important. Let's
use the new nice suffix.

diff --git a/mkosi.default.d/10-systemd.conf b/mkosi.conf.d/10-systemd.conf
similarity index 100%
rename from mkosi.default.d/10-systemd.conf
rename to mkosi.conf.d/10-systemd.conf

diff --git a/mkosi.default.d/arch/10-mkosi.arch b/mkosi.conf.d/arch/10-mkosi.arch
similarity index 100%
rename from mkosi.default.d/arch/10-mkosi.arch
rename to mkosi.conf.d/arch/10-mkosi.arch

diff --git a/mkosi.default.d/centos_epel/10-mkosi.centos_epel b/mkosi.conf.d/centos_epel/10-mkosi.centos_epel
similarity index 100%
rename from mkosi.default.d/centos_epel/10-mkosi.centos_epel
rename to mkosi.conf.d/centos_epel/10-mkosi.centos_epel

diff --git a/mkosi.default.d/debian/10-mkosi.debian b/mkosi.conf.d/debian/10-mkosi.debian
similarity index 100%
rename from mkosi.default.d/debian/10-mkosi.debian
rename to mkosi.conf.d/debian/10-mkosi.debian

diff --git a/mkosi.default.d/fedora/10-mkosi.fedora b/mkosi.conf.d/fedora/10-mkosi.fedora
similarity index 100%
rename from mkosi.default.d/fedora/10-mkosi.fedora
rename to mkosi.conf.d/fedora/10-mkosi.fedora

diff --git a/mkosi.default.d/opensuse/10-mkosi.opensuse b/mkosi.conf.d/opensuse/10-mkosi.opensuse
similarity index 100%
rename from mkosi.default.d/opensuse/10-mkosi.opensuse
rename to mkosi.conf.d/opensuse/10-mkosi.opensuse

diff --git a/mkosi.default.d/ubuntu/10-mkosi.ubuntu b/mkosi.conf.d/ubuntu/10-mkosi.ubuntu
similarity index 100%
rename from mkosi.default.d/ubuntu/10-mkosi.ubuntu
rename to mkosi.conf.d/ubuntu/10-mkosi.ubuntu