contrib/docker-compose: fixing mount that overrides containers' /etc (#6656)

The mount in the form of ./matrix-config:/etc overwrites the contents of the container /etc folder. Since all valid ca certificates are stored in /etc, the synapse.push.httppusher, for example, cannot validate the certificate from matrix.org.

changelog.d/6656.doc

+No more overriding the entire /etc folder of the container in docker-compose.yaml. Contributed by Fabian Meyer.

contrib/docker/docker-compose.yml

@@ -18,7 +18,7 @@ services:
       - SYNAPSE_CONFIG_PATH=/etc/homeserver.yaml
     volumes:
       # You may either store all the files in a local folder
-      - ./matrix-config:/etc
+      - ./matrix-config/homeserver.yaml:/etc/homeserver.yaml
       - ./files:/data
       # .. or you may split this between different storage points
       # - ./files:/data