app/matrix: migrate postgres and data to waw3

The way this was migrated is not to be spoken of.

(hint: it involved downtime, and mounting two volumes at once)

appservice-irc has some storage, we should migrate that to waw3, too. But
it's not as critical.

The new storage (waw3) is _much_ faster.

Change-Id: I4b4bd32e4fedc514753d25bac35d001e8a9c5f00
diff --git a/app/matrix/homeserver.yaml b/app/matrix/homeserver.yaml
index 1553053..0f23064 100644
--- a/app/matrix/homeserver.yaml
+++ b/app/matrix/homeserver.yaml
@@ -31,7 +31,7 @@
     user: "synapse"

     password: "{{ POSTGRES_PASSWORD }}"

     database: "synapse"

-    host: "postgres"

+    host: "waw3-postgres"

     port: "5432"

     cp_min: 5

     cp_max: 10