feat(12.2-01): add deferred:purge, its daily framework schedule and relation child hooks

- deferred:purge [--days] in lagoon.RuntimeCommands (purge_days, default 5)
- lagoon.FrameworkSchedule entry at purge_at (default 03:00, empty disables)
- conga prepends framework entries as summercms.lagoon[i]:<command>
- pact.Relation{Before,After}{Create,Update,Delete} optional hooks
- lagoon, conga and pact READMEs, scheduling and setup docs

docs/plugins/scheduling.md

@@ -66,6 +66,18 @@ Each run is a job on the `scheduled` queue with a single attempt: an interrupted
 
 The worker runs in `serve` by default. When you run workers separately (`queue.work_in_serve` set to `false`), `./bin/acme queue:work` carries the schedule too.
 
+## The framework's own schedule
+
+The framework schedules one command of its own: `deferred:purge`, which deletes the uploads and related records that admin forms left pending more than five days ago. It runs daily at 03:00 in `app.timezone`, with the ID `summercms.lagoon[0]:deferred:purge`, listed before the plugin entries. Set `database.deferred_bindings.purge_at` to another `HH:MM` time to move it, or to an empty string to remove it, for example when system cron runs `deferred:purge` instead:
+
+```yaml
+database:
+  deferred_bindings:
+    purge_at: "04:30"
+```
+
+A value that is not `HH:MM` fails the worker start with an error naming the key.
+
 ## Running the scheduler on its own
 
 To run only the scheduler in its own process, use `schedule:run`. It starts a worker on the `scheduled` queue and runs until it receives SIGINT or SIGTERM: