appservice: add and use homeserver_container_* vars (#2045)

* appservice: add and use matrix_homeserver_* vars

* appservice: use the new vars

* Apply suggestions from code review

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

roles/matrix-synapse/defaults/main.yml

@@ -61,8 +61,19 @@ matrix_synapse_container_metrics_api_host_bind_port: ''
 matrix_synapse_container_manhole_api_host_bind_port: ''
 
 # A list of extra arguments to pass to the container
+# Also see `matrix_synapse_container_arguments`
 matrix_synapse_container_extra_arguments: []
 
+# matrix_synapse_container_runtime_injected_arguments is a list of extra arguments to pass to the container.
+# This list is built during runtime. You're not meant to override this variable.
+# If you'd like to inject your own arguments, see `matrix_synapse_container_extra_arguments`.
+matrix_synapse_container_runtime_injected_arguments: []
+
+# matrix_synapse_container_arguments holds the final list of extra arguments to pass to the container.
+# You're not meant to override this variable.
+# If you'd like to inject your own arguments, see `matrix_synapse_container_extra_arguments`.
+matrix_synapse_container_arguments: "{{ matrix_synapse_container_extra_arguments + matrix_synapse_container_runtime_injected_arguments }}"
+
 # List of systemd services that matrix-synapse.service depends on
 matrix_synapse_systemd_required_services_list: ['docker.service']
 
@@ -324,8 +335,19 @@ matrix_synapse_additional_loggers: []
 # A list of appservice config files (in-container filesystem paths).
 # This list gets populated dynamically based on Synapse extensions that have been enabled.
 # You may wish to use this together with `matrix_synapse_container_additional_volumes` or `matrix_synapse_container_extra_arguments`.
+# Also see `matrix_synapse_app_service_config_files_final`
 matrix_synapse_app_service_config_files: []
 
+# matrix_synapse_app_service_runtime_injected_config_files is a list of appservice config files.
+# This list is built during runtime. You're not meant to override this variable.
+# If you'd like to inject your own arguments, see `matrix_synapse_app_service_config_files`.
+matrix_synapse_app_service_runtime_injected_config_files: []
+
+# matrix_synapse_app_service_config_files_final holds the final list of config files to pass to the container.
+# You're not meant to override this variable.
+# If you'd like to inject your own arguments, see `matrix_synapse_app_service_config_files`.
+matrix_synapse_app_service_config_files_final: "{{ matrix_synapse_app_service_config_files + matrix_synapse_app_service_runtime_injected_config_files }}"
+
 # This is set dynamically during execution depending on whether
 # any password providers have been enabled or not.
 matrix_synapse_password_providers_enabled: false

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

@@ -1647,7 +1647,7 @@ room_prejoin_state:
 
 # A list of application service config files to use
 #
-app_service_config_files: {{ matrix_synapse_app_service_config_files|to_json }}
+app_service_config_files: {{ matrix_synapse_app_service_config_files_final|to_json }}
 
 # Uncomment to enable tracking of application service IP addresses. Implicitly
 # enables MAU tracking for application service users.

roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2

@@ -39,7 +39,7 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name {{ matrix_synapse_wor
 			{% for volume in matrix_synapse_container_additional_volumes %}
 			-v {{ volume.src }}:{{ volume.dst }}:{{ volume.options }} \
 			{% endfor %}
-			{% for arg in matrix_synapse_container_extra_arguments %}
+			{% for arg in matrix_synapse_container_arguments %}
 			{{ arg }} \
 			{% endfor %}
 			{{ matrix_synapse_docker_image }} \

roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2

@@ -57,7 +57,7 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-synapse \
 			{% for volume in matrix_synapse_container_additional_volumes %}
 			-v {{ volume.src }}:{{ volume.dst }}:{{ volume.options }} \
 			{% endfor %}
-			{% for arg in matrix_synapse_container_extra_arguments %}
+			{% for arg in matrix_synapse_container_arguments %}
 			{{ arg }} \
 			{% endfor %}
 			{{ matrix_synapse_docker_image }} \