Add customizable ulimit settings for all Docker containers

Add ulimits as a configurable advanced setting for every container,
allowing customization through the web UI. Move hardcoded ulimits
from elasticsearch and zeek into defaults.yaml and fix elasticsearch
ulimits that were incorrectly nested under the environment key.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

salt/elasticagent/enabled.sls

@@ -54,6 +54,12 @@ so-elastic-agent:
       - {{ XTRAENV }}
         {% endfor %}
       {% endif %}
+    {% if DOCKER.containers['so-elastic-agent'].ulimits %}
+    - ulimits:
+    {%   for ULIMIT in DOCKER.containers['so-elastic-agent'].ulimits %}
+      - {{ ULIMIT }}
+    {%   endfor %}
+    {% endif %}
     - require:
       - file: create-elastic-agent-config
       - file: trusttheca