Defined the DependencyKey public protocol.

Sources/Dependencies/Protocols/DependencyKey.swift

@@ -0,0 +1,22 @@
+//
+//  DependencyKey.swift
+//  Dependencies
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+/// This protocol defines a key to use in the dependency service.
+public protocol DependencyKey {
+    
+    // MARK: Associated types
+    
+    /// The associated type representing the type of the dependency key's value.
+    associatedtype Value
+    
+    // MARK: Properties
+    
+    /// The default value for the dependency key.
+    static var currentValue: Value { get set }
+    
+}