feat: add PROSODY_DEBUG env var for debug logging

Set PROSODY_DEBUG=true to switch the prosody.log level from info to
debug. This makes stanza-too-large rejections and XML parse errors
visible — both are logged at debug level and otherwise invisible.

Usage in k8s:
  env:
  - name: PROSODY_DEBUG
    value: "true"

Part-of: <http://gitlab.vnc.biz/uxf/vnctalk-prosody/-/merge_requests/3>

config/prosody.cfg.lua.template

@@ -109,9 +109,10 @@ admin_socket = "/var/log/prosody/prosody.sock"
 --------------------------------------------------------------------------------
 
 -- The supported levels are: "debug", "info", "warn", "error".
+-- Set PROSODY_DEBUG=true in the environment to enable debug logging.
 log = {
 --  levels = { "info", "warn", "error" }, to = "console" ;
-  info = "/var/log/prosody/prosody.log";
+  ${PROSODY_LOG_LEVEL} = "/var/log/prosody/prosody.log";
   error = "/var/log/prosody/prosody.err";
 }
 

config/startup.sh

@@ -69,6 +69,15 @@ if [ -z "$S2S_STANZA_SIZE_LIMIT" ]; then
 fi
 export S2S_STANZA_SIZE_LIMIT
 
+# Logging level for prosody.log. Set PROSODY_DEBUG=true to enable debug
+# logging (shows stanza-too-large rejections, XML parse errors, etc.).
+if [ "$PROSODY_DEBUG" = "true" ]; then
+  PROSODY_LOG_LEVEL="debug"
+else
+  PROSODY_LOG_LEVEL="info"
+fi
+export PROSODY_LOG_LEVEL
+
 chmod 444 /etc/prosody/certs/prosody-ssl.pem
 chmod 444 /etc/prosody/certs/prosody-ssl.key