Basic application setup (#1)

This PR contains the work done to define the necessary setup from which the app will be built upon.

To provide further details on what has been done:
* created the app, the unit tests and the UI tests targets in the Xcode project;
* updated the bundle identifiers and OS deployment targets of all targets;
* added a `.gitignore` file tailored specifically for the project;
* added a `README` file that defines in details the goal of the project;
* added the [Swift Format](https://github.com/swiftlang/swift-format) rules that the source code should abide to;
* cleaned the boilerplate source code on all targets.

Reviewed-on: rock-n-code/todos-app#1
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

App/Sources/App/TodosApp.swift

@@ -0,0 +1,26 @@
+import SwiftData
+import SwiftUI
+
+@main
+struct TodosApp: App {
+    var sharedModelContainer: ModelContainer = {
+        let schema = Schema([
+            Item.self
+        ])
+        let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)
+
+        do {
+            return try ModelContainer(for: schema, configurations: [modelConfiguration])
+        }
+        catch {
+            fatalError("Could not create ModelContainer: \(error)")
+        }
+    }()
+
+    var body: some Scene {
+        WindowGroup {
+            ContentView()
+        }
+        .modelContainer(sharedModelContainer)
+    }
+}