Add initial dbus interface xml descripiton.

Much of this will change, but needed something to start with.
Based on notes at https://gitlab.steamos.cloud/jupiter/tasks/-/issues/894
Use objectserver to get introspection done for us.
Change to session bus for now since system bus will need
a config file to allow us to take the name. Will add later.
Implement one quick say_hello dbus method to start.
Add copyright headers.

src/manager.rs

@@ -0,0 +1,38 @@
+/*
+ * Copyright © 2023 Collabora Ltd.
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+use zbus_macros::dbus_interface;
+use zbus::{ObjectServer, SignalContext, MessageHeader};
+pub struct SMManager {
+
+}
+
+#[dbus_interface(name = "com.steampowered.SteamOSManager1")]
+impl SMManager {
+    async fn say_hello(&self, name: &str) -> String {
+        format!("Hello {}!", name)
+    }
+}
+