mkosi: Add number prefixes to per-distro files for easier overriding

This allows developers to add override files to override per-distro settings.

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

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

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

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

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