Added Telegram App as a Source

lib/app_sources/telegramapp.dart

@@ -0,0 +1,43 @@
+import 'package:easy_localization/easy_localization.dart';
+import 'package:html/parser.dart';
+import 'package:http/http.dart';
+import 'package:obtainium/custom_errors.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class TelegramApp extends AppSource {
+  TelegramApp() {
+    host = 'telegram.org';
+    name = 'Telegram ${tr('app')}';
+  }
+
+  @override
+  String standardizeURL(String url) {
+    return 'https://$host';
+  }
+
+  @override
+  String? changeLogPageFromStandardUrl(String standardUrl) => null;
+
+  @override
+  Future<APKDetails> getLatestAPKDetails(
+    String standardUrl,
+    Map<String, dynamic> additionalSettings,
+  ) async {
+    Response res = await get(Uri.parse('https://t.me/s/TAndroidAPK'));
+    if (res.statusCode == 200) {
+      var http = parse(res.body);
+      var messages =
+          http.querySelectorAll('.tgme_widget_message_text.js-message_text');
+      var version = messages.isNotEmpty
+          ? messages.last.innerHtml.split('\n').first.trim().split(' ').first
+          : null;
+      if (version == null) {
+        throw NoVersionError();
+      }
+      String? apkUrl = 'https://telegram.org/dl/android/apk';
+      return APKDetails(version, [apkUrl], AppNames('Telegram', 'Telegram'));
+    } else {
+      throw getObtainiumHttpError(res);
+    }
+  }
+}