Switch mjolnir-antispam from using spam_checker to modules

`spam_checker` has been deprecated for quite a while.
While it still probably works and while newer versions of
mjolnir-antispam still use it, we should switch to the new API.

roles/custom/matrix-synapse/defaults/main.yml

@@ -840,7 +840,16 @@ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_usernames: false
 # these rooms.
 # ["!roomid:example.org"]
 matrix_synapse_ext_spam_checker_mjolnir_antispam_config_ban_lists: []
-
+# A dictionary with various fields controlling max length.
+# See https://github.com/matrix-org/mjolnir/blob/main/docs/synapse_module.md for details.
+matrix_synapse_ext_spam_checker_mjolnir_antispam_config_message_max_length: {}
+# Actual configuration passed to the mjolnir-antispam Synapse module
+matrix_synapse_ext_spam_checker_mjolnir_antispam_config:
+  block_invites: "{{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_invites }}"
+  block_messages: "{{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_messages }}"
+  block_usernames: "{{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_usernames }}"
+  ban_lists: "{{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_ban_lists }}"
+  message_max_length: "{{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_message_max_length }}"
 
 # Enable this to activate the E2EE disabling Synapse module.
 # See: https://github.com/digitalentity/matrix_encryption_disabler

roles/custom/matrix-synapse/tasks/ext/mjolnir-antispam/setup_install.yml

@@ -14,18 +14,13 @@
   become_user: "{{ matrix_synapse_username }}"
 
 - ansible.builtin.set_fact:
-    matrix_synapse_spam_checker: >
+    matrix_synapse_modules: >
       {{
-        matrix_synapse_spam_checker
+        matrix_synapse_modules | default([])
         +
         [{
-          "module": "mjolnir.AntiSpam",
-          "config": {
-            "block_invites": matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_invites,
-            "block_messages": matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_messages,
-            "block_usernames": matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_usernames,
-            "ban_lists": matrix_synapse_ext_spam_checker_mjolnir_antispam_config_ban_lists,
-          }
+          "module": "mjolnir.Module",
+          "config": matrix_synapse_ext_spam_checker_mjolnir_antispam_config,
         }]
       }}