BUG/MEDIUM: mux-h1: don't send chunked responses to HTTP/1.0 clients

BUG/MEDIUM: mux-h1: don't send chunked responses to HTTP/1.0 clients

When a response without content-length is sent to an H1 client, the chunked
transfer-coding is added if the response is in HTTP/1.1, and a chunked
response is forwarded as-is. But the version which matters here is the
request's one: the chunked transfer-coding must not be sent in a response to
an HTTP/1.0 request (RFC9112#6.1), since such a client doesn't know about
it.

Now, on the frontend side, when the request was not HTTP/1.1 and the
response has a body without content-length, it is switched to an unknown
transfer length: no transfer-encoding header is emitted, the payload is sent
close-delimited (trailers are dropped) and the close mode is forced. For
bodyless responses (HEAD, 204, 304), only the transfer-encoding header is
removed.

A reg-test was added for this.

This patch must be backported to all supported versions.