pw: Set media.category property to manager

This will make the session manager give Helvum full permissions even when
used from flatpak or otherwise restricted, so that we can always change
the graph even if permissions become more restricted in the future.

src/pipewire_connection/mod.rs

@@ -65,7 +65,9 @@ pub(super) fn thread_main(
 
     while !is_stopped.get() {
         // Try to connect
-        let core = match context.connect(None) {
+        let core = match context.connect(Some(properties! {
+            "media.category" => "Manager"
+        })) {
             Ok(core) => Rc::new(core),
             Err(_) => {
                 if !is_connecting {