Changes docker network size to valid for docker compose

Docker compose plugin can't start using these configs because the network 10.20.20.0/16 is invalid and it expects either 10.20.0.0/16 or 10.20.20.0/24. Since we're using only three addresses and change only 4th octet, it's more viable to change the network to /24.
Relevant issue: #602

Author: aseliverstov-pinely

configs/demo/default/docker-compose.yml

@@ -67,4 +67,4 @@ networks:
     driver: bridge
     ipam:
       config:
-        - subnet: 10.20.20.0/16
+        - subnet: 10.20.20.0/24

configs/testing/e2e/docker-compose.yml

@@ -92,4 +92,4 @@ networks:
     driver: bridge
     ipam:
       config:
-        - subnet: 10.20.20.0/16
+        - subnet: 10.20.20.0/24

configs/testing/e2e_postgres/docker-compose.yml

@@ -96,4 +96,4 @@ networks:
     driver: bridge
     ipam:
       config:
-        - subnet: 10.20.20.0/16
+        - subnet: 10.20.20.0/24