So, I tested the new http2.conf file added by Xavier in commit e46a27465
It's working, but, the problem is that apache automatically de-activates the http2 module when using mpm_prefork (which is the default mpm module shipped within debian).
In such case, the following line appears in the apache error file upon startup:
Fri Nov 30 10:19:53.070367 2018] [http2:warn] [pid 14772] AH10034: The mpm module (prefork.c) is not supported by mod_http2. The mpm determines how things are processed in your server. HTTP/2 has more demands in this regard and the currently selected mpm will just not do. This is an advisory warning. Your server will continue to work, but the HTTP/2 protocol will be inactive.
I would say that additional comments in the http2.conf to inform about this limitation would be a good thing.
We could also include the configuration within a <IfModule ! mpm_prefork></IfModule>.