Add `matrix_authentication_service_admin_api_enabled` that controls if the Matrix Authentication Service's API is enabled

Builds up on top of d0adc8a374

roles/custom/matrix-authentication-service/defaults/main.yml

@@ -326,6 +326,8 @@ matrix_authentication_service_config_http_listener_web_resources_default: |-
       {'name': 'graphql'},
       {'name': 'assets'},
     ]
+    +
+    [{'name': 'adminapi'} if matrix_authentication_service_admin_api_enabled else []]
   }}
 matrix_authentication_service_config_http_listener_web_resources_auto: []
 matrix_authentication_service_config_http_listener_web_resources_custom: []
@@ -625,6 +627,10 @@ matrix_authentication_service_syn2mas_subcommand_extra_options: []
 # - avoid setting up the "compatibility layer" (that is, avoid installing container labels that capture login endpoints like `/_matrix/client/*/login`, etc.)
 matrix_authentication_service_migration_in_progress: false
 
+# Controls whether the admin API is enabled.
+# Ref: https://element-hq.github.io/matrix-authentication-service/topics/admin-api.html#enabling-the-api
+matrix_authentication_service_admin_api_enabled: false
+
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