Track device IDs for pushers (#13831)

Second half of the MSC3881 implementation

synapse/storage/schema/main/delta/73/03pusher_device_id.sql

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+/* Copyright 2022 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- Add a device_id column to track the device ID that created the pusher. It's NULLable
+-- on purpose, because a) it might not be possible to track down the device that created
+-- old pushers (pushers.access_token and access_tokens.device_id are both NULLable), and
+-- b) access tokens retrieved via the admin API don't have a device associated to them.
+ALTER TABLE pushers ADD COLUMN device_id TEXT;