Major Description
Currently, Pulsar exposes the message written count metrics though the Prometheus endpoint, and the metrics maintain in the broker, no been persistent. So if the topic ownership changes or restart broker, this will lead to reset the message written count of the topic to 0. This will confused users and not able to get the correct message written count metrics.
PIP-70 https://github.com/apache/pulsar/wiki/PIP-70%3A-Introduce-lightweight-broker-entry-metadata Introduced a broker level entry metadata which can support message index for a topic(or message offset of a topic), this will provide the ability to calculate the precise message written count for a topic. So we can leverage PIP-70 to improve the message written count metrics for the topic
