New plugin that queries the unsandbox API to determine which pool
a service is on, then routes to that pool's SSHPiper.
This enables multi-pool SSH routing from a single edge SSHPiper.
Usage:
sshpiperd api --api-url http://cammy.foxhop.net:8080 \
--upstream-key /path/to/key \
--cammy-host cammy.foxhop.net:2222 \
--ai-host ai.foxhop.net:2222
