Introduce a pulsar log4j2 appender (#1316)

### Motivation

when developing `pulsar-functions`, it would be good to log the log messages generated by functions to pulsar, so the user can easily tail the log messages topic to get all the messages per functions.

### Modifications

This PR is to add a pulsar based appender.

### Result

We are able to use pulsar log4j2 appender to log messages.
8 files changed