Move warning of open registration to v1.56 upgrade notes (#12322)

CHANGES.md

 Synapse 1.56.0rc1 (2022-03-29)
 ==============================
+Synapse will now refuse to start up if open registration is enabled, in order to help mitigate
+abuse across the federation. If you would like
+to provide registration to anyone, consider adding [email](https://github.com/matrix-org/synapse/blob/8a519f8abc6de772167c2cca101d22ee2052fafc/docs/sample_config.yaml#L1285),
+[recaptcha](https://matrix-org.github.io/synapse/v1.56/CAPTCHA_SETUP.html)
+or [token-based](https://matrix-org.github.io/synapse/v1.56/usage/administration/admin_api/registration_tokens.html) verification
+in order to prevent automated registration from bad actors.
+
+This check can be disabled by setting the `enable_registration_without_verification` option in your
+homeserver configuration file to `true`. More details are available in the
+[upgrade notes](https://matrix-org.github.io/synapse/v1.56/upgrade.html#open-registration-without-verification-is-now-disabled-by-default).
+
 Features
 --------
@@ -33,7 +44,7 @@ Internal Changes
 - Rename `shared_rooms` to `mutual_rooms` ([MSC2666](https://github.com/matrix-org/matrix-doc/pull/2666)), as per proposal changes. ([\#12036](https://github.com/matrix-org/synapse/issues/12036))
 - Remove check on `update_user_directory` for shared rooms handler ([MSC2666](https://github.com/matrix-org/matrix-doc/pull/2666)), and update/expand documentation. ([\#12038](https://github.com/matrix-org/synapse/issues/12038))
 - Refactor `create_new_client_event` to use a new parameter, `state_event_ids`, which accurately describes the usage with [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) instead of abusing `auth_event_ids`. ([\#12083](https://github.com/matrix-org/synapse/issues/12083), [\#12304](https://github.com/matrix-org/synapse/issues/12304))
-- Refuse to start if registration is enabled without email, captcha, or token-based verification unless the new config flag `enable_registration_without_verification` is set. ([\#12091](https://github.com/matrix-org/synapse/issues/12091))
+- Refuse to start if registration is enabled without email, captcha, or token-based verification unless the new config flag `enable_registration_without_verification` is set to `true`. ([\#12091](https://github.com/matrix-org/synapse/issues/12091))
 - Add tests for database transaction callbacks. ([\#12198](https://github.com/matrix-org/synapse/issues/12198))
 - Handle cancellation in `DatabasePool.runInteraction`. ([\#12199](https://github.com/matrix-org/synapse/issues/12199))
 - Add missing type hints for cache storage. ([\#12216](https://github.com/matrix-org/synapse/issues/12216))

changelog.d/12322.misc

+Refuse to start if registration is enabled without email, captcha, or token-based verification unless new config flag `enable_registration_without_verification` is set to `true`.
\ No newline at end of file

docs/upgrade.md

@@ -87,6 +87,11 @@ process, for example:
 
 # Upgrading to v1.56.0
 
+## Open registration without verification is now disabled by default
+
+Synapse will refuse to start if registration is enabled without email, captcha, or token-based verification unless the new config
+flag `enable_registration_without_verification` is set to "true".
+
 ## Groups/communities feature has been deprecated
 
 The non-standard groups/communities feature in Synapse has been deprecated and will
@@ -108,12 +113,6 @@ for more information and instructions on how to fix a database with incorrect va
 
 # Upgrading to v1.55.0
 
-## Open registration without verification is now disabled by default
-
-Synapse will refuse to start if registration is enabled without email, captcha, or token-based verification unless the new config 
-flag `enable_registration_without_verification` is set to "true".
-
-
 ## `synctl` script has been moved
 
 The `synctl` script