Fix `toString()` method in configuration implementations

[ppkarwasz]

Description

PR #2941 introduces some basic logging of the most important Configuration lifecycle events at an INFO level. The messages are meant to convey:

• which configuration file is used.
• the last modification timestamp of the file to distinguish between two revisions of the same file.

Unfortunately this information only appears in XmlConfiguration:

logging-log4j2/log4j-core/src/main/java/org/apache/logging/log4j/core/config/xml/XmlConfiguration.java

Lines 340 to 343 in 86781fd

	public String toString() {
	return getClass().getSimpleName() + "[location=" + getConfigurationSource() + ", lastModified="
	+ Instant.ofEpochMilli(getConfigurationSource().getLastModified()) + "]";
	}

JsonConfiguration only prints the name of the configuration file, while PropertiesConfiguration does not have a toString() method at all:

2025-04-04T19:10:16.058147325Z pool-10-thread-1 INFO Stopping configuration org.apache.logging.log4j.core.config.properties.PropertiesConfiguration@18765d9b...
2025-04-04T19:10:16.058147313Z pool-9-thread-1 INFO Stopping configuration org.apache.logging.log4j.core.config.properties.PropertiesConfiguration@18f5f66d...
2025-04-04T19:10:16.058631896Z pool-10-thread-1 INFO Configuration org.apache.logging.log4j.core.config.properties.PropertiesConfiguration@18765d9b stopped.
2025-04-04T19:10:16.058880638Z pool-9-thread-1 INFO Configuration org.apache.logging.log4j.core.config.properties.PropertiesConfiguration@18f5f66d stopped.

We probably should add the toString() method to AbstractConfiguration and remove it from its derived classes.

[anindita-sarkarArray]

@ppkarwasz I have made the requested changes. #3658 Please review

[garydgregory]

Why? This is not better since are now loosing information that was previously provided.

[anindita-sarkarArray]

hi @garydgregory , instead of AbstractConfiguration , shall I put my changes to all derived classes so that it can retain the additional info of subclasses.
OR
in addition to adding in AbstractConfiguration, I will modify the subclasses already having toString to have additional properties like [location=" + getConfigurationSource() + ", lastModified="
+ Instant.ofEpochMilli(getConfigurationSource().getLastModified())