shut down HTTPClient in example (#4)

* HTTPClient needs to be shutdown after use to avoid memory leak

See https://github.com/swift-server/async-http-client/blob/main/README.md#request-response-api

* need to shutdown the HTTPClient before each exit call

Not really recommended programming, but it is to demonstrate the shutdown of the HTTPClient before terminating the program.

* use defer to shutdown the HTTPClient

* http client shutdown in example

---------

Co-authored-by: Simon Leeb <52261246+sliemeobn@users.noreply.github.com>

Author: ronnybremer

Examples/PrintPDF/app.swift

@@ -0,0 +1,63 @@
+import Foundation
+import IppClient
+
+@main
+struct App {
+    static func main() async throws {
+        let httpClient = HTTPClient(configuration: .init(certificateVerification: .none))
+
+        do {
+            let printer = IppPrinter(
+                httpClient: httpClient,
+                uri: "ipps://macmini.not.local/printers/EPSON_XP_7100_Series"
+            )
+
+            let attributesResponse = try await printer.getPrinterAttributes()
+
+            if let printerName = attributesResponse[printer: \.printerName],
+               let printerState = attributesResponse[printer: \.printerState],
+               let printerStateReasons = attributesResponse[printer: \.printerStateReasons]
+            {
+                print("Printing on \(printerName) in state \(printerState), state reasons \(printerStateReasons)")
+            } else {
+                print("Could not read printer attributes, status code \(attributesResponse.statusCode)")
+            }
+
+            let pdf = try Data(contentsOf: URL(fileURLWithPath: "Examples/PrintPDF/hi_mom.pdf"))
+
+            let response = try await printer.printJob(
+                documentFormat: "application/pdf",
+                data: .bytes(pdf)
+            )
+
+            guard response.statusCode == .successfulOk, let jobId = response[job: \.jobId] else {
+                print("Print job failed with status \(response.statusCode)")
+                exit(1)
+            }
+
+            let job = printer.job(jobId)
+
+            while true {
+                let response = try await job.getJobAttributes(requestedAttributes: [.jobState])
+                guard let jobState = response[job: \.jobState] else {
+                    print("Failed to get job state")
+                    exit(1)
+                }
+
+                switch jobState {
+                case .aborted, .canceled, .completed:
+                    print("Job ended with state \(jobState)")
+                    exit(0)
+                default:
+                    print("Job state is \(jobState)")
+                }
+
+                try await Task.sleep(nanoseconds: 3_000_000_000)
+            }
+        } catch {
+            print("Error: \(error)")
+        }
+
+        try await httpClient.shutdown()
+    }
+}