Merge tag 'v1.12.1'

Synapse 1.12.1 (2020-04-02)
===========================

No significant changes since 1.12.1rc1.

Synapse 1.12.1rc1 (2020-03-31)
==============================

Bugfixes
--------

- Fix starting workers when federation sending not split out. ([\#7133](https://github.com/matrix-org/synapse/issues/7133)). Introduced in v1.12.0.
- Avoid importing `sqlite3` when using the postgres backend. Contributed by David Vo. ([\#7155](https://github.com/matrix-org/synapse/issues/7155)). Introduced in v1.12.0rc1.
- Fix a bug which could cause outbound federation traffic to stop working if a client uploaded an incorrect e2e device signature. ([\#7177](https://github.com/matrix-org/synapse/issues/7177)). Introduced in v1.11.0.

* tag 'v1.12.1':
  1.12.1
  Note where bugs were introduced
  1.12.1rc1
  Newsfile
  Rewrite changelog
  Add changelog
  Only import sqlite3 when type checking
  Fix another instance
  Only setdefault for signatures if device has key_json
  Fix starting workers when federation sending not split out.