Add App-Version HttpHeaderType to header method in HttpHeadersInjector

[ortegadn]

Actualmente en el HttpHeaderInjector se puede definir el valor del HttpHeaderType.appVersion, pero en el método de headers no se encuentra contemplado (tampoco los headers extras):

  Future<Map<String, String>> headers({Map<String, String>? extra}) async {
    final acceptLanguage = await getHeader(HttpHeaderType.acceptLanguage.key) ??
        extra?[HttpHeaderType.acceptLanguage.key];
    final authToken = extra?[HttpHeaderType.authorization.key] ??
        await getHeader(HttpHeaderType.authorization.key);
    final xToken = extra?[HttpHeaderType.xToken.key] ??
        await getHeader(HttpHeaderType.xToken.key);
    final accept = extra?[HttpHeaderType.accept.key] ?? 'application/json';
    final contentType =
        extra?[HttpHeaderType.contentType.key] ?? 'application/json';

    return {
      HttpHeaderType.accept.key: accept,
      HttpHeaderType.contentType.key: contentType,
      if (acceptLanguage != null)
        HttpHeaderType.acceptLanguage.key: acceptLanguage,
      if (xToken != null && xToken.isNotEmpty)
        HttpHeaderType.xToken.key: xToken,
      if (authToken != null && authToken.isNotEmpty)
        HttpHeaderType.authorization.key: authToken,
    };
  }