MEDIUM: mux-h1: Expose h1 in the list of supported mux protocols

MEDIUM: mux-h1: Expose h1 in the list of supported mux protocols

Add "h1" in the list of supported mux protocols. It relies on the H1
multiplexer and use the almost the same mux_ops structure. Only the flags
differ because this "new" mux does not support the upgrades.

Thus it is now possible to set "proto h1" or "check-proto h1" on bind/server
lines, depending on the context. However, when set, no upgrade to HTTP/2 is
performed. It may be a way to disable implicit HTTP/2 upgrades per bind
line.