[feat][misc] PIP-264: Add OpenTelemetry HTTP rate limiting filter metric

[dragosvictor]

PIP-264

Motivation

Adds metrics for the HTTP RateLimitingFilter class, currently exposed as Prometheus metric pulsar_broker_http_rejected_requests (ref).

Modifications

• Added metrics, as described by [feat][doc] PIP-264: Add OpenTelemetry HTTP rate limiting metrics reference pulsar-site#944, to the OpenTelemetry pipeline.
• Deviating from the exiting design, the new metric exposes counters for both accepted and rejected requests. The cost for doing this is very small, and we get increased visibility into the server.
• Note this PR only exposes these values for the broker. The proxy and function worker integration will be done separately.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Updated tests WebServiceTest#testRateLimiting to validate the metric counts.

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 OpenTelemetry HTTP rate limiting metrics reference pulsar-site#944
• Anything that affects deployment

Documentation

• doc
• doc-required [feat][doc] PIP-264: Add OpenTelemetry HTTP rate limiting metrics reference pulsar-site#944
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: dragosvictor#43