LibCore: Add Core::Group abstraction for group management :^)

This adds the Core::Group C++ abstraction to ease interaction with the
group entry database, as well as represent the Group entry.

Core::Group abstraction currently contains the following functionality:
- Add a group entry - 'Core::Group::add_group()'

Userland/Libraries/LibCore/Group.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2022, Kenneth Myhra <kennethmyhra@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/String.h>
+#include <AK/Vector.h>
+#include <grp.h>
+
+namespace Core {
+
+class Group {
+public:
+#ifndef AK_OS_MACOS
+    static ErrorOr<void> add_group(Group& group);
+#endif
+
+    Group() = default;
+    Group(String name, gid_t id = 0, Vector<String> members = {});
+
+    ~Group() = default;
+
+    String const& name() const { return m_name; }
+    void set_name(String const& name) { m_name = name; }
+
+    gid_t id() const { return m_id; }
+    void set_group_id(gid_t const id) { m_id = id; }
+
+    Vector<String>& members() { return m_members; }
+
+private:
+    static ErrorOr<bool> name_exists(StringView name);
+    static ErrorOr<bool> id_exists(gid_t id);
+    ErrorOr<struct group> to_libc_group();
+
+    String m_name;
+    gid_t m_id { 0 };
+    Vector<String> m_members;
+};
+
+}