Fіx possible OOM in downloadFileAsStreamAsync

[aNNiMON]

I've been using the -Xmx80M JVM option since telegrambots 5.x. Recently I got an OOM error on telegrambots 8.0.0 after trying to download a 17.8M file:

Exception in thread "OkHttp Dispatcher" java.lang.OutOfMemoryError: Java heap space
    at org.apache.commons.io.IOUtils.byteArray(IOUtils.java:368)
    at org.apache.commons.io.output.AbstractByteArrayOutputStream.toByteArrayImpl(AbstractByteArrayOutputStream.java:201)                                                             
    at org.apache.commons.io.output.UnsynchronizedByteArrayOutputStream.toByteArray(UnsynchronizedByteArrayOutputStream.java:184)                                                     
    at org.apache.commons.io.IOUtils.toByteArray(IOUtils.java:2703)                      
    at org.telegram.telegrambots.client.okhttp.OkHttpFutureDownloadCallback.onResponse(OkHttpFutureDownloadCallback.java:28)                                                          

This PR fixes the issue

[rubenlagus]

Please add a test inside TestTelegramClientIntegration to ensure it works as expected

[aNNiMON]

@rubenlagus tests have been added.

Now I see there are two possible usages of downloadFileAsStreamAsync:

1. As a callback chain: client.downloadFileAsStreamAsync(..).thenAccept(is -> /* read file */).then(...)
2. Get InputStream from completableFuture: InputStream is = client.downloadFileAsStreamAsync(...).get().

The problem with the second usage is that we cannot get the InputStream out of the completableFuture without closing the InputStream/responseBody in the OkHttpFutureDownloadCallback.

By making the InputStream buffered, we can safely return a stream from completableFuture:

InputStream is = client.downloadFileAsStreamAsync(...)..thenApply(is -> {
    try {
        return IOUtils.toBufferedInputStream(is);
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}).get();

I've done this for InputStream downloadFileAsStream(File file), but users should do the same if they use client.downloadFileAsStreamAsync(...).get().

---

I also though replacing complete(body.byteStream()); with complete(IOUtils.toBufferedInputStream(body.byteStream()));, but it still consumes additional memory.

Here are my observations for downloading 18_439_895 bytes:

• complete(new ByteArrayInputStream(IOUtils.toByteArray(body.byteStream()))); -> OOM on -Xmx80M:
• complete(IOUtils.toBufferedInputStream(body.byteStream())); -> Works on -Xmx80M, OOM on -Xmx40M:
• complete(body.byteStream()); -> works -Xmx80M as well as -Xmx40M