Clusterred appender should consider the categories.

It turns out that whenever the clusterred appender is used the log event is passed to all actual appenders.
The actual appender's category is ignored. This commit proposes a fix so that log events are sent only to those appenders that either have this category or do not have a category set. This is the same behavior like in non-cluster environment.

Signed-off-by: Vladimir Mitev <idalv@users.noreply.github.com>