Add first-class JSON log output (Log4j2 JsonTemplateLayout) via env var #3870

Enhancement Type

Improve an existing feature

Describe the enhancement

Describe the problem / motivation
Many log pipelines and docker observation tools work best with JSON in container stdout. Today the image primarily supports customizing PatternLayout via LOG_CONSOLE_FORMAT / LOG_FILE_FORMAT, which still produces unstructured text. (docker-minecraft-server.readthedocs.io)

Proposed enhancement
Add an opt-in way to switch console (and optionally file) logs to JSON output using Log4j2’s JsonTemplateLayout. (logging.apache.org)

Suggested UX:

• LOG_FORMAT=json (or LOG_LAYOUT=json-template)
• LOG_JSON_TEMPLATE=<builtin name | path>