Update VPN user agent (#971)

Required:

Task/Issue URL: https://app.asana.com/0/1207162258152427/1207484485195971/f
iOS PR: duckduckgo/iOS#3302
macOS PR: duckduckgo/macos-browser#3181
What kind of version bump will this require?: Patch

Description:

This PR updates the VPN client to read from APIRequest.Headers when setting up requests.

Later, the client class should be refactored to use APIRequest across the board for increased testability, but for now I'm reusing a pattern used in a number of places in the clients.

Package.swift

@@ -323,6 +323,7 @@ let package = Package(
             dependencies: [
                 .target(name: "WireGuardC"),
                 "Common",
+                "Networking"
             ],
             swiftSettings: [
                 .define("DEBUG", .when(configuration: .debug))

Sources/NetworkProtection/Networking/NetworkProtectionClient.swift

@@ -17,6 +17,8 @@
 //
 
 import Foundation
+import Networking
+import os.log
 
 protocol NetworkProtectionClient {
     func getLocations(authToken: String) async -> Result<[NetworkProtectionLocation], NetworkProtectionClientError>
@@ -244,6 +246,7 @@ final class NetworkProtectionBackendClient: NetworkProtectionClient {
 
     func getLocations(authToken: String) async -> Result<[NetworkProtectionLocation], NetworkProtectionClientError> {
         var request = URLRequest(url: locationsURL)
+        request.allHTTPHeaderFields = APIRequest.Headers().httpHeaders
         request.setValue("bearer \(authToken)", forHTTPHeaderField: "Authorization")
         let downloadedData: Data
 
@@ -287,6 +290,7 @@ final class NetworkProtectionBackendClient: NetworkProtectionClient {
 
     func getServers(authToken: String) async -> Result<[NetworkProtectionServer], NetworkProtectionClientError> {
         var request = URLRequest(url: serversURL)
+        request.allHTTPHeaderFields = APIRequest.Headers().httpHeaders
         request.setValue("bearer \(authToken)", forHTTPHeaderField: "Authorization")
         let downloadedData: Data
 
@@ -330,6 +334,7 @@ final class NetworkProtectionBackendClient: NetworkProtectionClient {
 
     func getServerStatus(authToken: String, serverName: String) async -> Result<NetworkProtectionServerStatus, NetworkProtectionClientError> {
         var request = URLRequest(url: serverStatusURL(serverName: serverName))
+        request.allHTTPHeaderFields = APIRequest.Headers().httpHeaders
         request.setValue("bearer \(authToken)", forHTTPHeaderField: "Authorization")
         let downloadedData: Data
 
@@ -382,6 +387,7 @@ final class NetworkProtectionBackendClient: NetworkProtectionClient {
         }
 
         var request = URLRequest(url: registerKeyURL)
+        request.allHTTPHeaderFields = APIRequest.Headers().httpHeaders
         request.setValue("bearer \(authToken)", forHTTPHeaderField: "Authorization")
         request.addValue("application/json", forHTTPHeaderField: "Content-Type")
         request.httpMethod = "POST"
@@ -444,6 +450,7 @@ final class NetworkProtectionBackendClient: NetworkProtectionClient {
         }
 
         var request = URLRequest(url: endpoint)
+        request.allHTTPHeaderFields = APIRequest.Headers().httpHeaders
         request.addValue("application/json", forHTTPHeaderField: "Content-Type")
         request.httpMethod = "POST"
         request.httpBody = requestBodyData