Is your feature request related to a problem? Please describe.
PgCat, unlike Pgbouncer, doesn't support UNIX sockets, neither to connect to servers nor to expose itself to applications.
UNIX sockets allow for a slightly better latency, and allow the use of file-level authentication.

Describe the solution you'd like
PgCat should be able to connect to PostgreSQL instances using UNIX sockets.
PgCat should be reachable through UNIX sockets.

Describe alternatives you've considered
None

Additional context
None