Support overriding the Log4j configuration file location

[dlvenable]

Is your feature request related to a problem? Please describe.

A Data Prepper administrator can change the log4j file. But it is not possible to override the value.

Describe the solution you'd like

Allow setting the configuration file via JAVA_OPTS. See the following:

env JAVA_OPTS="-Dlog4j.configurationFile=custom/path/to/log4j2-rolling.properties" ./bin/data-prepper

Data Prepper already has the JAVA_OPTS environment variable. However, it does not support changing this value. This is because Data Prepper overrides that value.

Describe alternatives you've considered (Optional)

There could be a data-prepper-config.yaml configuration. However, this would come much later and isn't how the current Log4j configuration works.

[dlvenable]

As seen below, the DATA_PREPPER_JAVA_OPTS environment variable sets the Log4j configuration file. However, it is set after JAVA_OPTS and thus overrides what the Data Prepper admin sets.

data-prepper/release/archives/linux/data-prepper-jdk-x64.sh

Lines 37 to 40 in c04a46b

	DATA_PREPPER_JAVA_OPTS="-Dlog4j.configurationFile=$DATA_PREPPER_HOME/config/log4j2-rolling.properties"
	if [[ $# == 0 ]]; then
	exec java $JAVA_OPTS $DATA_PREPPER_HOME_OPTS $DATA_PREPPER_JAVA_OPTS -cp "$DATA_PREPPER_CLASSPATH" org.opensearch.dataprepper.DataPrepperExecute