[BUG] Set pulsar event time when it exceed zero.

[syhily]

Describe the bug

A clear and concise description of what the bug is. DynamicPulsarSerializationSchema.java wrongly add even time when it was zero.

if (eventTime != null && eventTime >= 0) {

This is not allowed in Pulsar's TypedMessageBuilderImpl.java.

checkArgument(timestamp > 0, "Invalid timestamp : '%s'", timestamp);

[nikolasten]

How to workaround this? Its fixed in latest snapshot, but not in stable release https://issues.apache.org/jira/browse/FLINK-28506