allow direction of when a service can be deleted

LoopKit/Pluggable.swift

@@ -13,8 +13,13 @@ public protocol Pluggable: AnyObject {
     /// A plugin may need a reference to another plugin. This callback allows for such a reference.
     /// It is called once during app initialization after plugins are initialized and again as new plugins are added and initialized.
     func initializationComplete(for pluggables: [Pluggable])
+
+    /// A plugin may require another plugin. This callback informs this dependency.
+    /// Often this is called as apart of `initializationComplete(for pluggables: [Pluggable])`
+    func isDependency(_ isDependency: Bool)
 }
 
 public extension Pluggable {
     func initializationComplete(for pluggables: [Pluggable]) { } // optional
+    func isDependency(_ isDependency: Bool) { } // optional
 }