Support reset cursor by message index

Currently, Pulsar supports resetting the cursor according to time and message-id, e.g. you can reset the cursor to 3 hours ago or reset the cursor to a specific message-id. For some cases that users want to reset to the 10,000 earlier messages, Pulsar has not supported this operation yet

PIP-70 https://github.com/apache/pulsar/wiki/PIP-70%3A-Introduce-lightweight-raw-Message-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 support reset cursor according to the message index.