Add Apache Pulsar monitoring integration

[otisg]

See:

• https://pulsar.apache.org/docs/en/deploy-monitoring/
• https://pulsar.apache.org/docs/en/administration-stats/
  Note that metrics are exposed in Prometheus format, so maybe that's the thing to tackle first: Add Prometheus/OpenMetrics support sematext-agent-java#24

Note from https://pulsar.apache.org/docs/en/deploy-monitoring/

When collecting time series statistics, the major problem is to make sure the number of dimensions attached to the data does not explode. For that reason we only collect time series of metrics aggregated at the namespace level.