Update docker.io/library/postgres Docker tag to v15

By default the limit on file descriptors is at a 1024 hard limit and 520k hard limit.
Unsure how this affects nginx, but each client connection needs two file descriptors.
So let's try to set the limit of open files explicitly.

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:15-alpine
     volumes:
       - /opt/mailman/database:/var/lib/postgresql/data
     networks:

resources/chaosknoten/public-reverse-proxy/nginx/nginx.conf

@@ -3,6 +3,7 @@
 
 user  nginx;
 worker_processes  auto;
+worker_rlimit_nofile  2050; # should be worker_connections*2 at least
 
 error_log  /var/log/nginx/error.log notice;
 pid        /var/run/nginx.pid;