Make use of matrix_host_command_docker instead of hardcoding

roles/matrix-postgres/tasks/util/create_additional_databases.yml

@@ -1,7 +1,6 @@
 ---
-
 - name: Retrieve IP of postgres container
-  shell: "docker inspect matrix-postgres | jq -r '.[0].NetworkSettings.Networks.{{ matrix_docker_network }}.IPAddress'"
+  shell: "{{ matrix_host_command_docker }} inspect matrix-postgres | jq -r '.[0].NetworkSettings.Networks.{{ matrix_docker_network }}.IPAddress'"
   register: matrix_postgres_container_ip
 
 - name: Create additional users in postgres