internal/outcome: expose pipewire via pipewire-pulse

This no longer exposes the pipewire socket to the container, and instead mediates access via pipewire-pulse. This makes insecure parts of the protocol inaccessible as explained in the doc comment in hst.

Closes #29.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/outcome/outcome.go

@@ -257,6 +257,10 @@ type outcomeStateParams struct {
 	// Populated by spRuntimeOp.
 	runtimeDir *check.Absolute
 
+	// Path to pipewire-pulse server.
+	// Populated by spPipeWireOp if DirectPipeWire is false.
+	pipewirePulsePath *check.Absolute
+
 	as hst.ApplyState
 	*outcomeState
 }