Merge #460: backups: bring in line with upstream duplicity

5bee663 backups: bring in line with upstream duplicity (nixbitcoin)

Pull request description:

ACKs for top commit:
  erikarvstedt:
    ACK 5bee663
  jonasnick:
    ACK 5bee663

Tree-SHA512: 5dc3e7e0522d5a7039868ed84f6849ff561c194fa5d9c17c217fa22e89b1ed3636eba8c14ed92f91c63ce9199f03411266c602ee8339e773e8f48599f520e208

modules/backups.nix

@@ -3,7 +3,16 @@
 with lib;
 let
   options.services.backups = {
-    enable = mkEnableOption "Backups service";
+    enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Enable backups of node data.
+        This uses the NixOS duplicity service.
+        To further configure the backup, you can set NixOS options `services.duplicity.*`.
+        The `services.duplicity.cleanup.*` options are particularly useful.
+      '';
+    };
     with-bulk-data = mkOption {
       type = types.bool;
       default = false;
@@ -87,8 +96,8 @@ in {
         enable = true;
         extraFlags = [
           "--include-filelist" "${filelist}"
-          "--full-if-older-than" "1M"
         ];
+        fullIfOlderThan = mkDefault "1M";
         targetUrl = cfg.destination;
         frequency = cfg.frequency;
         secretFile = "${config.nix-bitcoin.secretsDir}/backup-encryption-env";