add a script to generate new signing_key files

changelog.d/5361.feature

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+Add a script to generate new signing-key files.

scripts/generate_signing_key.py

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+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+# Copyright 2019 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.
+import argparse
+import sys
+
+from signedjson.key import write_signing_keys, generate_signing_key
+
+from synapse.util.stringutils import random_string
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+
+    parser.add_argument(
+        "-o", "--output_file",
+
+        type=argparse.FileType('w'),
+        default=sys.stdout,
+        help="Where to write the output to",
+    )
+    args = parser.parse_args()
+
+    key_id = "a_" + random_string(4)
+    key = generate_signing_key(key_id),
+    write_signing_keys(args.output_file, key)