feat(ops/dns): Import tvl.fyi DNS zone into depot

Imports the current state of the tvl.fyi zone and configures simple CI
checks on the file format.

No deployment automation exists for this (yet?).

Change-Id: Ia7d72e02b9f6d3adef994c5dc1898cc0df9dfcfb
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2600
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: sterni <sternenseemann@systemli.org>

ops/dns/default.nix

@@ -0,0 +1,14 @@
+# Performs simple (local-only) validity checks on DNS zones.
+{ pkgs, ... }:
+
+let
+  checkZone = zone: file: pkgs.runCommandNoCC "${zone}-check" {} ''
+    ${pkgs.bind}/bin/named-checkzone -i local ${zone} ${file} | tee $out
+  '';
+
+  zones = {
+    tvl-fyi = checkZone "tvl.fyi" ./tvl.fyi.zone;
+  };
+in zones // {
+  meta.targets = builtins.attrNames zones;
+}