refactor(ops): Use besadii configuration from agenix

We already checked this in, but this commit adds the configuration for
making use of it.

There are two copies of besadii's JSON configuration with different
permissions.

Note that the buildkite-graphql-token path needs to be updated in
static-pipeline.yml, but this needs to happen in a separate commit
after deploy because the pipeline will break otherwise.

Change-Id: I6fab4bf1a2e679df7cf76521e2b53bd9dadbac62

ops/modules/monorepo-gerrit.nix

@@ -5,7 +5,7 @@ let
   cfg = config.services.gerrit;
 
   besadiiWithConfig = name: pkgs.writeShellScript "besadii-whitby" ''
-    export BESADII_CONFIG=/etc/secrets/besadii.json
+    export BESADII_CONFIG=/run/agenix/gerrit-besadii-config
     exec -a ${name} ${depot.ops.besadii}/bin/besadii "$@"
   '';