basic: add RuntimeScope enum

In various tools and services we have a per-system and per-user concept.
So far we sometimes used a boolean indicating whether we are in system
mode, or a reversed boolean indicating whether we are in user mode, or
the LookupScope enum used by the lookup path logic.

Let's address that, in introduce a common enum for this, we can use all
across the board.

This is mostly just search/replace, no actual code changes.

src/basic/runtime-scope.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <errno.h>
+
+#include "macro.h"
+
+typedef enum RuntimeScope {
+        RUNTIME_SCOPE_SYSTEM,           /* for the system */
+        RUNTIME_SCOPE_USER,             /* for a user */
+        RUNTIME_SCOPE_GLOBAL,           /* for all users */
+        _RUNTIME_SCOPE_MAX,
+        _RUNTIME_SCOPE_INVALID = -EINVAL,
+} RuntimeScope;
+
+const char *runtime_scope_to_string(RuntimeScope scope) _const_;
+RuntimeScope runtime_scope_from_string(const char *s) _const_;