[Java] make java worker log file prefix (default to java-worker) configurable

[jiafuzha]

Description

For java worker, it's log file always being prefixed with "java-worker". And in python log_monitor.py, it hardcodes "java-worker*.log" to be polled for new log msg periodically. Some configs, like log_to_driver and RAY_BACKEND_LOG_LEVEL, don't prevent the log monitor from polling and publishing logs to gcs. To save some CPU cycle and network bandwidth, especially if there is large amount of logs produced from JVM, we can have an option. like a JVM system property, to set log file prefix for java worker instead of hard coded to "java-worker".

Use case

For RayDP, there are large number of INFO logs generated by Spark executor. The logs are useful but no need to be log-monitored by ray. We can rename ray java worker log file to be prefixed with something else other than 'java-worker'. Then, ray log monitor will not poll logs from the log files.