DDSSEC12 — Provide pre-shared protection for unauthenticated messages

There is an inherent DoS network amplification attack that exploits peer-to-peer discovery. See https://issues.omg.org/browse/DDSIRTP26-6

This issue should be addressed by DDS-Security. Likely using some pre-shared key mechanics to protect all messages not otherwise protected. For example, the authentication handshakes.

Provide a layer of PSK protection

Peovide the means to use a pre-shared secret to protect any RTPS message (e.g. bootstrap messges) that is not otherwise protected by the keys that the DomainParticipants exchange.

Also define the "pre-shared" key mechanism as a separate "builtin" plugin