Log4j2Metrics does not work with programatically added LoggerConfig

[pativa]

Describe the bug

This is a follow-up issue to #5756 .
In that issue, rebinding when log4j2 Configuration is reloaded was fixed.

However, there is also a case when the existing instance of Configuration is updated with a new LoggerConfig programatically, without actually creating a new Configuration instance. This does not work due to the comparison of oldValue with newValue here:

micrometer/micrometer-core/src/main/java/io/micrometer/core/instrument/binder/logging/Log4j2Metrics.java

Line 99 in 04f6d8c

if (listener.getNewValue() instanceof Configuration && listener.getOldValue() != listener.getNewValue()) {

Currently the logic for rebinding will only reload if a new Configuration instance is loaded, so an added logger to the existing Configuration will not get a MetricsFilter added, even if updateLoggers() is called.

For an example of when this might be done in real code, setting log levels in the loggers endpoint of Spring Boot Actuator can create a new LoggerConfiguration on an existing Configuration.

I will provide a PR together with a test that shows when it does not work.