Update Logback and Log4j2 integrations to support structured logging.
Support for the ECS and Logstash JSON formats is provided out-of-the-box
and the `StructuredLogFormatter` interface may be used to if further
custom formats need to be supported.
Closes gh-5479
Co-authored-by: Phillip Webb <phil.webb@broadcom.com>
Moritz Halbritter