[CAMEL-6694] Allow user to pass logger instance in camel-log endpoint
URI

The URI has form: log:logger-name?level=info&logger=#mylogger

"mylogger" is registered in context's registry
[CAMEL-6694] lookup logger in registry when single instance available
[CAMEL-6694] Added OSGi integration tests for logging with MDC SIFT logger
Merge branch 'CAMEL-6694' of https://github.com/grgrzybek/camel
CAMEL-6694: Fixed CS