Update docker.io/library/postgres Docker tag to v18

Also start documenting the docs structure in home.

docs/index.md

@@ -1,3 +1,5 @@
 # CCCHH Infrastructure Documentation
 
 Home for CCCHH infrastructure documentation.
+
+- **Guides**: Documentation on how to achieve various things.

inventories/chaosknoten/host_vars/cloud.yaml

@@ -1,7 +1,7 @@
 # renovate: datasource=docker depName=git.hamburg.ccc.de/ccchh/oci-images/nextcloud
 nextcloud__version: 32
 # renovate: datasource=docker depName=docker.io/library/postgres
-nextcloud__postgres_version: 15.17
+nextcloud__postgres_version: 18.4
 nextcloud__fqdn: cloud.hamburg.ccc.de
 nextcloud__data_dir: /data/nextcloud
 nextcloud__extra_configuration: "{{ lookup('ansible.builtin.template', 'resources/chaosknoten/cloud/nextcloud/extra_configuration.config.php.j2') }}"

resources/chaosknoten/lists/docker_compose/compose.yaml.j2

@@ -62,7 +62,7 @@ services:
       - POSTGRES_DB=mailmandb
       - POSTGRES_USER=mailman
       - "POSTGRES_PASSWORD={{ secret__lists__postgres_password }}"
-    image: docker.io/library/postgres:12-alpine
+    image: docker.io/library/postgres:18-alpine
     volumes:
       - /opt/mailman/database:/var/lib/postgresql/data
     networks:

resources/chaosknoten/pretalx/docker_compose/compose.yaml.j2

@@ -3,7 +3,7 @@
 
 services:
   database:
-    image: docker.io/library/postgres:15-alpine
+    image: docker.io/library/postgres:18-alpine
     environment:
       - "POSTGRES_USER=pretalx"
       - "POSTGRES_PASSWORD={{ secret__pretalx_db_password }}"