Dynamic log configuration APIs don't allow setting the log level for loggers that aren't explicitly configured

[yashmayya]

• Support for dynamic log configuration APIs was added in Adding logger utils and allow change logger level at runtime #9180 and documented in add documentation for dynamic logging pinot-contrib/pinot-docs#132
• Currently, these APIs don't allow modifying the level of loggers that aren't explicitly configured.
• For instance, let's say that a Pinot controller process is started with the log4j configuration file containing log levels defined for the following loggers: root, org.apache.pinot.tools.admin and org.reflections (see this log4j config file for reference).
• Now, if we attempt to change the log level of the org.apache.pinot.controller.helix.core.realtime.SegmentCompletionManager class via PUT /loggers/org.apache.pinot.controller.helix.core.realtime.SegmentCompletionManager?level=DEBUG, this returns the following response: {"code":500,"error":"Logger - org.apache.pinot.controller.helix.core.realtime.SegmentCompletionManager not found"}
• This is because the check here only checks whether the logger name is in the list of loggers that are already explicitly configured.
• This severely limits the usefulness of the dynamic log configuration API as it prevents the modification of all loggers that aren't explicitly configured in the log4j configuration file.