Upgrade Synapse (1.54.0 -> 1.55.0)

`roles/matrix-synapse/vars/workers.yml` has not been updated here,
because running `roles/matrix-synapse/files/workers-doc-to-yaml.awk`
seems to cause some trouble with the current `workers.md` file
available at https://github.com/matrix-org/synapse/raw/master/docs/workers.md,
namely lots of:

> FIXME: ADDITIONAL CONDITIONS REQUIRED: to be enabled manually

lines and commented out regex lines.

This is something that remains to be investigated/fixed.

roles/matrix-synapse/defaults/main.yml

@@ -9,7 +9,7 @@ matrix_synapse_container_image_self_build_repo: "https://github.com/matrix-org/s
 
 matrix_synapse_docker_image: "{{ matrix_synapse_docker_image_name_prefix }}matrixdotorg/synapse:{{ matrix_synapse_docker_image_tag }}"
 matrix_synapse_docker_image_name_prefix: "{{ 'localhost/' if matrix_synapse_container_image_self_build else matrix_container_global_registry_prefix }}"
-matrix_synapse_version: v1.54.0
+matrix_synapse_version: v1.55.0
 matrix_synapse_docker_image_tag: "{{ matrix_synapse_version }}"
 matrix_synapse_docker_image_force_pull: "{{ matrix_synapse_docker_image.endswith(':latest') }}"
 

roles/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -1977,8 +1977,14 @@ saml2_config:
 #
 #             localpart_template: Jinja2 template for the localpart of the MXID.
 #                 If this is not set, the user will be prompted to choose their
-#                 own username (see 'sso_auth_account_details.html' in the 'sso'
-#                 section of this file).
+#                 own username (see the documentation for the
+#                 'sso_auth_account_details.html' template). This template can
+#                 use the 'localpart_from_email' filter.
+#
+#             confirm_localpart: Whether to prompt the user to validate (or
+#                 change) the generated localpart (see the documentation for the
+#                 'sso_auth_account_details.html' template), instead of
+#                 registering the account right away.
 #
 #             display_name_template: Jinja2 template for the display name to set
 #                 on first login. If unset, no displayname will be set.
@@ -3013,4 +3019,36 @@ redis:
   password: {{ matrix_synapse_redis_password }}
 
 
+## Background Updates ##
+
+# Background updates are database updates that are run in the background in batches.
+# The duration, minimum batch size, default batch size, whether to sleep between batches and if so, how long to
+# sleep can all be configured. This is helpful to speed up or slow down the updates.
+#
+background_updates:
+    # How long in milliseconds to run a batch of background updates for. Defaults to 100. Uncomment and set
+    # a time to change the default.
+    #
+    #background_update_duration_ms: 500
+
+    # Whether to sleep between updates. Defaults to True. Uncomment to change the default.
+    #
+    #sleep_enabled: false
+
+    # If sleeping between updates, how long in milliseconds to sleep for. Defaults to 1000. Uncomment
+    # and set a duration to change the default.
+    #
+    #sleep_duration_ms: 300
+
+    # Minimum size a batch of background updates can be. Must be greater than 0. Defaults to 1. Uncomment and
+    # set a size to change the default.
+    #
+    #min_batch_size: 10
+
+    # The batch size to use for the first iteration of a new background update. The default is 100.
+    # Uncomment and set a size to change the default.
+    #
+    #default_batch_size: 50
+
+
 # vim:ft=yaml