feat(ops/secrets): Use korora for type checking secrets

Type checking of secrets was removed in cff6575948 to get rid of yants.
This adds back type checking using Korora.

Fixes https://git.snix.dev/snix/snix/issues/71
Change-Id: I27cd47b7e1810be5c4cd5d86366e860ca217f9c4
Reviewed-on: https://cl.snix.dev/c/snix/+/30118
Tested-by: besadii
Reviewed-by: Ryan Lahfa <masterancpp@gmail.com>
Reviewed-by: Florian Klink <flokli@flokli.de>

third_party/korora/default.nix

@@ -0,0 +1,3 @@
+{ depot, ... }:
+
+import depot.third_party.sources.korora { }