DOC: quic: clarifies limited-quic support

DOC: quic: clarifies limited-quic support

This patch extends the documentation for "limited-quic" global keyword.
It mentions first that it relies on USE_QUIC_OPENSSL_COMPAT=1 build
option.

Compatibility with TLS libraries is now clearly exposed. In particular,
it highlights the fact that it is mostly targetted at OpenSSL version
prior to 3.5.2, and that it should be disabled if a recent OpenSSL
release is available. It also states that limited-quic does nothing if
USE_QUIC_OPENSSL_COMPAT is not set during compilation.