Switch UNIX socket paths to /run, and add a UNIX socket example for HAProxy (#16700)

changelog.d/16700.doc

+Switch the example UNIX socket paths to /run. Add HAProxy example configuration for UNIX sockets.

docs/reverse_proxy.md

@@ -181,7 +181,11 @@ frontend matrix-federation
 backend matrix
   server matrix 127.0.0.1:8008
 ```
-
+Example configuration, if using a UNIX socket. The configuration lines regarding the frontends do not need to be modified.
+```
+backend matrix
+  server matrix unix@/run/synapse/main_public.sock
+```
 
 [Delegation](delegate.md) example:
 ```

docs/usage/configuration/config_documentation.md

@@ -566,7 +566,7 @@ listeners:
   # Note that x_forwarded will default to true, when using a UNIX socket. Please see
   # https://matrix-org.github.io/synapse/latest/reverse_proxy.html.
   #
-  - path: /var/run/synapse/main_public.sock
+  - path: /run/synapse/main_public.sock
     type: http
     resources:
       - names: [client, federation]
@@ -4218,9 +4218,9 @@ Example configuration(#2, for UNIX sockets):
 ```yaml
 instance_map:
   main:
-    path: /var/run/synapse/main_replication.sock
+    path: /run/synapse/main_replication.sock
   worker1:
-    path: /var/run/synapse/worker1_replication.sock
+    path: /run/synapse/worker1_replication.sock
 ```
 ---
 ### `stream_writers`
@@ -4406,13 +4406,13 @@ Example configuration(#2, using UNIX sockets with a `replication` listener):
 ```yaml
 worker_listeners:
   - type: http
-    path: /var/run/synapse/worker_public.sock
+    path: /run/synapse/worker_replication.sock
     resources:
-      - names: [client, federation]
+      - names: [replication]
   - type: http
-    path: /var/run/synapse/worker_replication.sock
+    path: /run/synapse/worker_public.sock
     resources:
-      - names: [replication]
+      - names: [client, federation]
 ```
 ---
 ### `worker_manhole`