Configure apache reverse proxy for grpc connections via HTTP/2

HTTP/2 (TLS)
ProxyPass "/app" "h2://app.example.com"
ProxyPassReverse "/app" "https://app.example.com"

HTTP/2 (cleartext)
ProxyPass "/app" "h2c://app.example.com"
ProxyPassReverse "/app" "http://app.example.com"

References
https://httpd.apache.org/docs/2.4/mod/mod_proxy_http2.html