Relocate Postgres additional database creation logic

Moving it above the "uninstalling" set of tasks is better.
Extracting it out to another file at the same time, for readability,
especially given that it will probably have to become more complex in
the future (potentially installing `jq`, etc.)

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

@@ -0,0 +1,28 @@
+---
+
+- name: Retrieve IP of postgres container
+  shell: "docker inspect matrix-postgres | jq -r '.[0].NetworkSettings.Networks.{{ matrix_docker_network }}.IPAddress'"
+  register: matrix_postgres_container_ip
+
+- name: Create additional users in postgres
+  postgresql_user:
+    name: "{{ item.name }}"
+    password: "{{ item.pass }}"
+    login_host: "{{ matrix_postgres_container_ip.stdout }}"
+    login_port: 5432
+    login_user: "{{ matrix_postgres_connection_username }}"
+    login_password: "{{ matrix_postgres_connection_password }}"
+    login_db: "{{ matrix_postgres_db_name }}"
+  loop: matrix_postgres_additional_databases
+
+- name: Create additional users in postgres
+  postgresql_db:
+    name: "{{ item.name }}"
+    owner: "{{ item.name }}"
+    lc_ctype: 'C'
+    lc_collate: 'C'
+    login_host: "{{ matrix_postgres_container_ip.stdout }}"
+    login_port: 5432
+    login_user: "{{ matrix_postgres_connection_username }}"
+    login_password: "{{ matrix_postgres_connection_password }}"
+  loop: matrix_postgres_additional_databases