scope: allow unprivileged delegation on scopes

Previously it was possible to set delegate property for scope, but you
were not able to allow unprivileged process to manage the scope's cgroup
hierarchy. This is useful when launching manager process that  will run
unprivileged but is supposed to manage its own (scope) sub-hierarchy.

Fixes #21683

src/basic/unit-def.c

@@ -169,6 +169,7 @@ DEFINE_STRING_TABLE_LOOKUP(path_state, PathState);
 
 static const char* const scope_state_table[_SCOPE_STATE_MAX] = {
         [SCOPE_DEAD]         = "dead",
+        [SCOPE_START_CHOWN]  = "start-chown",
         [SCOPE_RUNNING]      = "running",
         [SCOPE_ABANDONED]    = "abandoned",
         [SCOPE_STOP_SIGTERM] = "stop-sigterm",

src/basic/unit-def.h

@@ -114,6 +114,7 @@ typedef enum PathState {
 
 typedef enum ScopeState {
         SCOPE_DEAD,
+        SCOPE_START_CHOWN,
         SCOPE_RUNNING,
         SCOPE_ABANDONED,
         SCOPE_STOP_SIGTERM,