example systemd config: propagate reloads to units (#9463)

It should be possible to reload `synapse.target` to have the reload propagate
to all the synapse units.

changelog.d/9463.doc

+Update the example systemd config to propagate reloads to individual units.

docs/systemd-with-workers/system/matrix-synapse-worker@.service

@@ -4,6 +4,7 @@ AssertPathExists=/etc/matrix-synapse/workers/%i.yaml
 
 # This service should be restarted when the synapse target is restarted.
 PartOf=matrix-synapse.target
+ReloadPropagatedFrom=matrix-synapse.target
 
 # if this is started at the same time as the main, let the main process start
 # first, to initialise the database schema.

docs/systemd-with-workers/system/matrix-synapse.service

@@ -3,6 +3,7 @@ Description=Synapse master
 
 # This service should be restarted when the synapse target is restarted.
 PartOf=matrix-synapse.target
+ReloadPropagatedFrom=matrix-synapse.target
 
 [Service]
 Type=notify