[feat][broker] PIP-264: Add replication metrics

[dragosvictor]

PIP-264

Motivation

Adds existing broker replicator metrics (documented by https://pulsar.apache.org/docs/next/reference-metrics/#replication-metrics-1) to the OpenTelemetry pipeline.

Modifications

• Adds the replication metrics, as described by [feat][doc] PIP-264: Add replication metrics reference apache/pulsar-site#926, to the collector runs.
• Renamed Replicator#getStats to Replicator#computeStats, as it modifies the underlying object in the process. Added a simple getter Replicator#getStats for the object itself. This helps clarify the intent of the methods.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Added test ReplicatorTest#testReplicationMetrics
• Updated test ReplicatorTest#testResumptionAfterBacklogRelaxed

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics: As described in [feat][doc] PIP-264: Add replication metrics reference apache/pulsar-site#926
• Anything that affects deployment

Documentation

• doc
• doc-required [feat][doc] PIP-264: Add replication metrics reference apache/pulsar-site#926
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: #26