Added (first version of) sample Hummingbird app. (#4)

This PR contains the work done to:
* Implemented a basic `Hummingbird` application in which to integrate the `HummingbirdDocC` library.
* Added the *ArgumentParser* package dependency to the `Package.swift` file;
* Added a new *sample* target to the `Package.swift` file;
* Added library and documentation tasks to the `Makefile` file.

Reviewed-on: #4
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Sources/HummingbirdDocC/Internal/Extensions/LoggerMetadata+Helpers.swift

@@ -0,0 +1,50 @@
+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import protocol Hummingbird.RequestContext
+
+import struct Hummingbird.HTTPResponse
+import struct Hummingbird.Request
+import struct Logging.Logger
+
+extension Logger.Metadata {
+    
+    // MARK: Functions
+    
+    /// Generates a dictionary to use as metadata for events to log into the logging system.
+    /// - Parameters:
+    ///   - context: A type that contains all the parameters associated with a given request, and that conforms to the `RequestContext` protocol.
+    ///   - request: A type that contains all the parameters to process as a request.
+    ///   - statusCode: A representation of a response status to provide as a response.
+    ///   - redirect: A URI path to use in a redirection event, if any.
+    /// - Returns: A generated metadata dictionary for an event to log into the logging system.
+    static func metadata(
+        context: any RequestContext,
+        request: Request,
+        statusCode: HTTPResponse.Status,
+        redirect: String? = nil
+    ) -> Self {
+        var metadata: Logger.Metadata = [
+            "hb.request.id": "\(context.id)",
+            "hb.request.method": "\(request.method.rawValue)",
+            "hb.request.path": "\(request.uri.path)",
+            "hb.request.status": "\(statusCode.code)"
+        ]
+        
+        if let redirect {
+            metadata["hb.request.redirect"] = "\(redirect)"
+        }
+        
+        return metadata
+    }
+    
+}