Offer a cababilty to disable structured logging

Thank you for the new integrated structured logging in Spring Boot 3.4. I have been very satisfied with its behaviour and the ergonomics of using it contrasted with having to wire that up, myself.

I would like to be able to explicitly disable it, though. I have a situation where, for safety purposes, the setting is distributed widely with

logging.structured.format.console=ecs

for correct default behaviour, but that leads to developers being unable to view plain text logs anywhere, namely during development, on account of the settings having no non-structured override option. The JSON logs are a lot more difficult to parse so that one use case has suffered considerably.

Before 3.4, we relied on a local

logging.config=

to disable a similarly distributed configuration and that worked well enough. Unfortunately there is no analogue for logging.structured.format.console that lets us do the same.

Start by tracing the logging.structured.format.console setting and compare it with the previously used logging.config= override described in the issue. Determine how an explicit local setting can disable the distributed structured format while preserving the default elsewhere. Done means developers can view plain-text console logs without removing the shared ECS configuration.