Add additional QUIC muxer to QUIC transport doc

[salmad3]

Done Criteria

• [x] Create an overview for "QUIC Native Stream Multiplexing" section

EDIT: Add a section further describing QUIC steam muxing.

Why Important

• Page was created as a placeholder and requires additional material.
• The doc serves a better purpose in being about native stream muxers (in general).

EDIT: Decided to just include this as part of the QUIC transport doc.

[marten-seemann]

Do you want to explain in detail how QUIC does stream multiplexing? I’m wondering if the libp2p docs are the right place for that, this seems very QUIC specific.

[salmad3]

Right along the same lines. Think it would be useful to have material that introduces having a transport with a native stream muxer, how it works/how it works in libp2p.