feat(tvldb): Import the tvldb/paroxysm source, add a Nix derivation

- This imports the tvldb (actually a thing called 'paroxysm') code
  from https://git.theta.eu.org/eta/paroxysm into the monorepo.
- Additionally, I did a nix thing, yay! \o/
  (well, with tazjin's help)
- 3p/default.nix needed modifying to whitelist pgsql.

Change-Id: Icdf13ca221650dde376f632bd2dd8a087af451bf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/389
Reviewed-by: tazjin <mail@tazj.in>

third_party/default.nix

@@ -98,6 +98,7 @@ let
       pandoc
       parallel
       pkgconfig
+      postgresql
       pounce
       python3
       python3Packages