[Library] iTunes library (#5)

This PR contains the work done to implement the `iTunesService` service that fetches the reviews from the **Apple App Store**.

Reviewed-on: rock-n-code/app-reviews#5
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Libraries/iTunes/Kit/Extensions/ServiceConfiguration+Inits.swift

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+//
+//  ServiceConfiguration+Inits.swift
+//  ReviewsiTunesKit
+//
+//  Created by Javier Cicchelli on 17/03/2024.
+//  Copyright © 2024 Röck+Cöde VoF. All rights reserved.
+//
+
+import Foundation
+import ReviewsFoundationKit
+import ReviewsFeedKit
+
+extension ServiceConfiguration {
+    
+    // MARK: Initialisers
+    init(session: URLSessionConfiguration = .ephemeral) {
+        self.init(
+            host: .iTunes,
+            session: session,
+            decoder: .default
+        )
+    }
+    
+}

Libraries/iTunes/Kit/Extensions/URL+Constants.swift

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+//
+//  URL+Constants.swift
+//  ReviewsiTunesKit
+//
+//  Created by Javier Cicchelli on 17/03/2024.
+//  Copyright © 2024 Röck+Cöde VoF. All rights reserved.
+//
+
+import Foundation
+import ReviewsFoundationKit
+
+extension URL {
+    
+    // MARK: Constants
+    static let iTunes: URL = .init(string: "https://itunes.apple.com") ?? .bitBucket
+    
+}