meson: create /var/log/journal/{,remote/} conditionally

meson: create /var/log/journal/{,remote/} conditionally

Not everybody has those dirs in the filesystem (and they don't need to).
When creating an installation package using $DESTDIR, it is easy enough to
remove or ignore those directories, but if installing into a real root, it
is ugly to create and remove them. Let's add an option so people can skip
it if they want.

Inspired by #12930.