Make synapse-s3-storage-provider periodic migration schedule customizable

Larger deployments may wish to run migration more often.

roles/custom/matrix-synapse/defaults/main.yml

@@ -874,6 +874,9 @@ matrix_synapse_ext_synapse_s3_storage_provider_config_threadpool_size: 40
 # It specifies how old files need to have been inactive to be eligible for migration from the local filesystem to the S3 data store.
 # By default, we use `0` which says "all files are eligible for migration".
 matrix_synapse_ext_synapse_s3_storage_provider_update_db_day_count: 0
+# Specifies how often periodic migration (`matrix-synapse-s3-storage-provider-migrate.timer`) will run.
+# This is a systemd timer OnCalendar definition. Learn more here: https://man.archlinux.org/man/systemd.time.7#CALENDAR_EVENTS
+matrix_synapse_ext_synapse_s3_storage_provider_periodic_migration_schedule: '*-*-* 05:00:00'
 
 matrix_s3_media_store_enabled: false
 matrix_s3_media_store_custom_endpoint_enabled: false

roles/custom/matrix-synapse/templates/synapse/ext/s3-storage-provider/systemd/matrix-synapse-s3-storage-provider-migrate.timer.j2

@@ -3,7 +3,7 @@ Description=Migrates locally-stored Synapse media store files to S3
 
 [Timer]
 Unit=matrix-synapse-s3-storage-provider-migrate.service
-OnCalendar=*-*-* 05:00:00
+OnCalendar={{ matrix_synapse_ext_synapse_s3_storage_provider_periodic_migration_schedule }}
 
 [Install]
 WantedBy=timers.target