Make LookupFilter compatible with log4j2-2.16 for lookup of the contextName

As of log4j2 2.16+, jndi based lookups are now by default disabled.
The most common usage thereof, for brXM, is specifically the lookup of the logging/contextName to filter log events for specific contexts, like with:

<LookupFilter key="jndi:logging/contextName" value="cms" onMatch="ACCEPT"/>

This specific jndi lookup is not a security vulnerability however, so to cater for log4j2 2.16+ with now default disabled jndi lookup,
a custom (fixed) workaround has been implemented which only intercepts a filter key="jndi:logging/contextName" and then do the jndi lookup directly, not via log4j2.