golem: add golem-provider clan module

clanModules/golem-provider/interface.nix

@@ -0,0 +1,20 @@
+{ lib, ... }:
+let
+  inherit (lib) mkOption;
+
+  inherit (lib.types) nullOr str;
+
+in
+{
+  options.clan.golem-provider = {
+    account = mkOption {
+      type = nullOr str;
+      description = ''
+        Ethereum address for payouts.
+
+        Leave empty to automatically generate a new address upon first start.
+      '';
+      default = null;
+    };
+  };
+}