docs/cmdline-opts: unify HTTP version style in --help output

docs/cmdline-opts: unify HTTP version style in --help output

$ curl -h all | grep -- --http

Now:

     --http0.9                      Allow HTTP/0.9 responses
 -0, --http1.0                      Use HTTP/1.0
     --http1.1                      Use HTTP/1.1
     --http2                        Use HTTP/2
     --http2-prior-knowledge        Use HTTP/2 without HTTP/1.1 Upgrade
     --http3                        Use HTTP/3
     --http3-only                   Use HTTP/3 only

Before:

     --http0.9                      Allow HTTP 0.9 responses
 -0, --http1.0                      Use HTTP 1.0
     --http1.1                      Use HTTP 1.1
     --http2                        Use HTTP/2
     --http2-prior-knowledge        Use HTTP 2 without HTTP/1.1 Upgrade
     --http3                        Use HTTP v3
     --http3-only                   Use HTTP v3 only

Closes #16542