Fix server crash when File-Based Debug Logger is enabled

When the debug logger is enabled, LoggerConfigManager sets root JUL level
to FINEST which makes Grizzly's DefaultFilterChain.executeFilter() check
isLoggable(FINEST)=true and log the FilterChainContext object.

In Grizzly 3.0.1, FilterChainContext.toString() has a bytecode bug where
it does a checkcast to char[] on the message field. When the message is
a LdapResponseMessage, the cast fails with ClassCastException that
propagates through the RxJava pipeline causing a server crash.

Fix: Limit org.glassfish.grizzly JUL logging to FINE level so that
isLoggable(FINEST) returns false, preventing the broken code path.

Also add toString() to LdapResponseMessage for better diagnostics.

Agent-Logs-Url: https://github.com/OpenIdentityPlatform/OpenDJ/sessions/73a4bf17-653a-4ea6-b379-6a220c9059db

Co-authored-by: vharseko <6818498+vharseko@users.noreply.github.com>