Add extension support for OpenTelemetryAppender so we can add custom formatting and logging.

[jsing120]

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

So the package io.opentelemetry.instrumentation.log4j.appender.v2_17.OpenTelemetryAppender uses io.opentelemetry.instrumentation.log4j.appender.v2_17.internal.LogEventMapper to map a logevent, however multiple initiatives would need capabilities to mask PII data or some custom formatting of data as part of the logevent. A feature to add a custom LogEvent or event a custom Logevent mapper would be nice to have.

Describe the solution you'd like

Make OpenTelemetryAppender extendible

Describe alternatives you've considered

If OpenTelemetryAppender had non private method and with a constructor we could have easily created a wrapper `
public class MaskingOpenTelemetryAppender extends OpenTelemetryAppender {

public MaskingOpenTelemetryAppender(/* all required args */) {
    super(/* pass all args to super */);
}

@Override
protected void emit(OpenTelemetry openTelemetry, LogEvent event) {
    // Mask the message before passing to the mapper
    String originalMessage = event.getMessage().getFormattedMessage();

//Some Custom masking logic
String maskedMessage = MaskLogMessageConverter.maskPII(originalMessage);

    // Create a new LogEvent with the masked message, or wrap the message
    // (You may need to create a new Message implementation with the masked string)
    LogEvent maskedEvent = new MaskedLogEvent(event, maskedMessage);

    // Call super.emit with the masked event
    super.emit(openTelemetry, maskedEvent);
}

}
package com.test.interceptor;

import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.message.Message;

public class MaskedLogEvent implements LogEvent {

private final LogEvent originalEvent;
private final String maskedMessage;

public MaskedLogEvent(LogEvent originalEvent, String maskedMessage) {
    this.originalEvent = originalEvent;
    this.maskedMessage = maskedMessage;
}

@Override
public Message getMessage() {
    return new Message() {
        @Override
        public String getFormattedMessage() {
            return maskedMessage;
        }

        @Override
        public String getFormat() {
            return originalEvent.getMessage().getFormat();
        }

        @Override
        public Object[] getParameters() {
            return originalEvent.getMessage().getParameters();
        }

        @Override
        public Throwable getThrowable() {
            return originalEvent.getMessage().getThrowable();
        }
    };
}

// Delegate all other methods to the original event
@Override
public LogEvent toImmutable() {
    return originalEvent.toImmutable();
}

@Override
public boolean isIncludeLocation() {
    return originalEvent.isIncludeLocation();
}

@Override
public void setIncludeLocation(boolean locationRequired) {
    originalEvent.setIncludeLocation(locationRequired);
}

@Override
public long getTimeMillis() {
    return originalEvent.getTimeMillis();
}

@Override
public void setTimeMillis(long timeMillis) {
    originalEvent.setTimeMillis(timeMillis);
}

@Override
public String getLoggerName() {
    return originalEvent.getLoggerName();
}

@Override
public org.apache.logging.log4j.Level getLevel() {
    return originalEvent.getLevel();
}

@Override
public Throwable getThrown() {
    return originalEvent.getThrown();
}

@Override
public Marker getMarker() {
    return originalEvent.getMarker();
}

@Override
public String getThreadName() {
    return originalEvent.getThreadName();
}

@Override
public long getThreadId() {
    return originalEvent.getThreadId();
}

@Override
public int getThreadPriority() {
    return originalEvent.getThreadPriority();
}

@Override
public StackTraceElement getSource() {
    return originalEvent.getSource();
}

@Override
public ReadOnlyStringMap getContextData() {
    return originalEvent.getContextData();
}

@Override
public Map<String, String> getContextMap() {
    return originalEvent.getContextMap();
}

@Override
public String getLoggerFqcn() {
    return originalEvent.getLoggerFqcn();
}

@Override
public boolean isEndOfBatch() {
    return originalEvent.isEndOfBatch();
}

@Override
public void setEndOfBatch(boolean endOfBatch) {
    originalEvent.setEndOfBatch(endOfBatch);
}

@Override
public long getNanoTime() {
    return originalEvent.getNanoTime();
}

}`

Additional context

No response