Merge tag 'v1.32.1'

Synapse 1.32.1 (2021-04-21)
===========================

This release fixes [a regression](https://github.com/matrix-org/synapse/issues/9853) in Synapse 1.32.0 that caused connected Prometheus instances to become unstable. If you ran Synapse 1.32.0 with Prometheus metrics, first upgrade to Synapse 1.32.1 and follow [these instructions](https://github.com/matrix-org/synapse/pull/9854#issuecomment-823472183) to clean up any excess writeahead logs.

Bugfixes
--------

- Fix a regression in Synapse 1.32.0 which caused Synapse to report large numbers of Prometheus time series, potentially overwhelming Prometheus instances. ([\#9854](https://github.com/matrix-org/synapse/issues/9854))