fix: make matrix_synapse_ext_synapse_s3_storage_provider_config_prefix be used

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

@@ -15,7 +15,7 @@ container_id=$(\
 	{{ arg }} \
 	{% endfor %}
 	{{ matrix_synapse_container_image_final }} \
-	-c 's3_media_upload update-db $UPDATE_DB_DURATION && s3_media_upload --no-progress check-deleted $MEDIA_PATH && s3_media_upload --no-progress upload $MEDIA_PATH $BUCKET --delete --storage-class $STORAGE_CLASS --endpoint-url $ENDPOINT {% if matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_enabled %}--sse-customer-algo $SSE_CUSTOMER_ALGO --sse-customer-key $SSE_CUSTOMER_KEY{% endif %}' \
+	-c 's3_media_upload update-db $UPDATE_DB_DURATION && s3_media_upload --no-progress check-deleted $MEDIA_PATH && s3_media_upload --no-progress upload $MEDIA_PATH $BUCKET --delete --storage-class $STORAGE_CLASS --endpoint-url $ENDPOINT {% if matrix_synapse_ext_synapse_s3_storage_provider_config_prefix %}--prefix $PREFIX {% endif %}{% if matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_enabled %}--sse-customer-algo $SSE_CUSTOMER_ALGO --sse-customer-key $SSE_CUSTOMER_KEY{% endif %}' \
 )
 
 {# We need to connect to the Postgres network, which should be in this list. #}

roles/custom/matrix-synapse/templates/synapse/ext/s3-storage-provider/media_storage_provider.yaml.j2

@@ -12,6 +12,9 @@ store_remote: {{ matrix_synapse_ext_synapse_s3_storage_provider_store_remote | t
 store_synchronous: {{ matrix_synapse_ext_synapse_s3_storage_provider_store_synchronous | to_json }}
 config:
   bucket: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_bucket | to_json }}
+{% if matrix_synapse_ext_synapse_s3_storage_provider_config_prefix %}
+  prefix: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_prefix | to_json }}
+{% endif %}
   region_name: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_region_name | to_json }}
   endpoint_url: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_endpoint_url | to_json }}
 {% if not matrix_synapse_ext_synapse_s3_storage_provider_config_ec2_instance_profile | bool %}