First iteration of RTSP endpoint functionality

[sgfn]

Rebased. Sorry for the inconvenience

[codecov[bot]]

Codecov Report

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[sgfn]

Fixes:

• Everything outlined by @mickel8 in his review
• Resolve race condition between :new_rtp_stream and :rtsp_setup_complete messages
• Add proposed solution to attempt to create client-side NAT binding