Minimal CA support

This verison has a worse UI, but also chnages the schema less: One
non-null constraint is removed, but no new columns are added.

Co-Authored-By: Andrea Ciceri <andrea.ciceri@autistici.org>
Co-Authored-By: regnat <rg@regnat.ovh>

t/jobs/config.nix.in

@@ -6,4 +6,9 @@ rec {
       system = builtins.currentSystem;
       PATH = path;
     } // args);
+  mkContentAddressedDerivation = args: mkDerivation ({
+    __contentAddressed = true;
+    outputHashMode = "recursive";
+    outputHashAlgo = "sha256";
+  } // args);
 }