[feat] [broker] expose out bytes and message metrics per topic

[pgier]

Add prometheus metrics which expose the per topic messages out and bytes out total on a per topic basis. Currently, only the subscription level stats are enabled.

Signed-off-by: Paul Gier paul.gier@datastax.com

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Motivation

There are currently two metrics pulsar_out_bytes_total and pulsar_out_messages_total. The metrics represent the pulsar stats on a per subscription basis. It would be convenient to be able to see the summary of these values per topic similar to the stats exposed by pulsar-admin.

Modifications

Added the two metrics and updated the test to verify that the output is correct.

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This change is already covered by existing tests, such as (please describe tests). I made an enhancement to the existing Promtheus metrics test.

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