add postgresql role for ens. psql and opt. some dbs and users are set up

Add postgresql role for ensuring postgresql is installed.
Furthermore the role optionally takes some basic configuration to ensure
databases with their owners and users are set up as specified.

This is a requirement for a new netbox role.

roles/postgresql/tasks/main.yaml

@@ -0,0 +1,28 @@
+- name: Ensure postgresql is installed
+  ansible.builtin.apt:
+    name:
+      - postgresql
+  become: true
+
+- name: Ensure Python library for community.postgresql is installed if needed
+  ansible.builtin.apt:
+    name:
+      - python3-psycopg
+  become: true
+  when: postgresql__dbs != [ ] or postgresql__users != [ ]
+
+- name: Ensure users
+  community.postgresql.postgresql_user:
+    name: "{{ item.name }}"
+    password: "{{ item.password | default('') }}"
+  become: true
+  become_user: postgres
+  loop: "{{ postgresql__users }}"
+
+- name: Ensure dbs with owners
+  community.postgresql.postgresql_db:
+    name: "{{ item.name }}"
+    owner: "{{ item.owner }}"
+  become: true
+  become_user: postgres
+  loop: "{{ postgresql__dbs }}"