Log4j2 - Support the use of async appenders when using the standard Pattern Layout

Original GTSE: https://new-relic.atlassian.net/jira/software/c/projects/NR/boards/289?selectedIssue=NR-323639

When using a Log4j async appender and the Pattern layout, trace id and span id are not properly added to the log event metadata because of a thread hop, which results in the active transaction no longer being available.

Module: https://github.com/newrelic/newrelic-java-agent/tree/main/instrumentation/apache-log4j-2.11

It might be possible to instrument a super class of the layout classes and instrument the toSerializable() method similarly to how the current AbstractJacksonLayout_Instrumentation is instrumented.

To enable async appenders in a project do the following:

• Create a file named log4j2.component.properties in the same folder where the log4j2.xml file exists
• Add the following line to the file:

Log4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector

An example log4j2.xml that configures a simple pattern layout with a console appender:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn">
  <Appenders>
    <Console name="console_log" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{yyyy-MM-dd'T'HH:mm:ss.SSSXXX},%-5p,%m%n" />
    </Console>
  </Appenders>
  <Loggers>
    <Root level="info">
      <AppenderRef ref="console_log" />
    </Root>
  </Loggers>
</Configuration>

https://new-relic.atlassian.net/browse/NR-323639

Start in instrumentation/apache-log4j-2.11 and read AbstractJacksonLayout_Instrumentation.java, focusing on how to instrument layout serialization. Investigate whether a superclass layout and its toSerializable() method can handle Pattern layouts across the async thread hop. Done means trace and span IDs are added to log event metadata when async appenders use the standard Pattern layout.