DevX: Add another Matrix site to docker-compose (#3511)

* remove redis, since we dont use it

* update localhost TLS certificat to add *.othersite.m.localhost wildcard

* allow for federation

* Add services and config files for Matrix site othersite.m.localhost

* add element web instance app.othersite.m.localhost

* update README

* exclude synapse database for othersite.m.localhost

* linting

playwright-backend-docker-compose.override.yml

@@ -2,3 +2,6 @@ services:
   synapse:
     volumes:
       - ./backend/playwright_homeserver.yaml:/data/cfg/homeserver.yaml:Z
+  synapse-1:
+    volumes:
+      - ./backend/playwright_homeserver-othersite.yaml:/data/cfg/homeserver.yaml:Z