restic: add --retry-lock=5m to all backup jobs

Prevents lock conflicts when multiple backup jobs targeting the same
repository run concurrently. Jobs will now retry acquiring the lock
every 10 seconds for up to 5 minutes before failing.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

hosts/ha1/configuration.nix

@@ -87,6 +87,7 @@
       "--keep-monthly 6"
       "--keep-within 1d"
     ];
+    extraOptions = [ "--retry-lock=5m" ];
   };
 
   # Open ports in the firewall.

hosts/monitoring01/configuration.nix

@@ -83,6 +83,7 @@
       "--keep-monthly 6"
       "--keep-within 1d"
     ];
+    extraOptions = [ "--retry-lock=5m" ];
   };
 
   services.restic.backups.grafana-db = {
@@ -100,6 +101,7 @@
       "--keep-monthly 6"
       "--keep-within 1d"
     ];
+    extraOptions = [ "--retry-lock=5m" ];
   };
 
   # Open ports in the firewall.