Add closeHttpClient to MinioAsyncClient.Builder #1586

In PR #1546 the logic was added to close httpClient when closing minio client.
However, if a custom httpClient is passed to the builder then closeHttpClient is set to false

Here is the code from MinioAsyncClient.java

boolean closeHttpClient = false;
  if (this.httpClient == null) {
    this.httpClient =
            HttpUtils.newDefaultHttpClient(
                    DEFAULT_CONNECTION_TIMEOUT, DEFAULT_CONNECTION_TIMEOUT, DEFAULT_CONNECTION_TIMEOUT);
    closeHttpClient = true;
}

So we set closeHttpClient to true only when httpClient is not passed to the builder and we create a default one

My proposal is to allow to pass closeHttpClient to the builder and even make it true by default
I can create PR for this if the idea is approved