user-classification: add new "foreign" UID range

This makes the UID range configurable via build time options, but of
course it really shouldn't be changed. The default range I picked is
outside even of IPAs current (ridiculously large) allocation ranges,
hence hopefully minimizes conflicts.

src/basic/uid-classification.c

@@ -127,5 +127,5 @@ bool uid_for_system_journal(uid_t uid) {
 
         /* Returns true if the specified UID shall get its data stored in the system journal. */
 
-        return uid_is_system(uid) || uid_is_dynamic(uid) || uid == UID_NOBODY || uid_is_container(uid);
+        return uid_is_system(uid) || uid_is_dynamic(uid) || uid == UID_NOBODY || uid_is_container(uid) || uid_is_foreign(uid);
 }