http2-client should use ALPNHandler

### Expected behavior

Failure to negotiate HTTP/2 should either be reported, or tolerated.

### Actual behavior

http2-client ignores the failure to negotiate HTTP/2 and just sends it anyway, leading to errors.

### Steps to reproduce

1. Attempt to reach https://amazon.com
2. Observe errors reported.

Start with the http2-client example and inspect how it configures or uses ALPNHandler. Reproduce the behavior against https://amazon.com and verify that failure to negotiate HTTP/2 is either reported or tolerated without sending HTTP/2 requests anyway.

Written by the indexing model from the issue text.