[improve][broker] Reduce number of OpenTelemetry consumer attributes

[dragosvictor]

Motivation

PR #22693 introduced OpenTelemetry consumer stats. Two issues surfaced as part of a follow-up review:

1. The attribute sets are immutable and should be cached, such that they are not allocated on each metric collection run.
2. Too many attributes are being exposed, potentially slowing down the metric pipeline as a result. Many of these attributes are currently being emitted as 'string' metrics in Prometheus.

Modifications

1. Cache the attribute sets in the Consumer class, using lazy initialization to conserve memory if OTel is disabled.
2. Remove consumer attributes pulsar.consumer.connected_since, pulsar.consumer.metadata, pulsar.client.address, and pulsar.client.version.
3. Extract attribute pulsar.consumer.blocked from metric "pulsar.broker.consumer.message.unack.count into its own metric pulsar.broker.consumer.blocked.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Updated test OpenTelemetryTopicStatsTest#testMessagingMetrics to account for these changes

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 above
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: dragosvictor#30

[dragosvictor]

@asafm Please take a look if this addresses your concerns. Thank you!

[lhotari]

LGTM

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 5 lines in your changes missing coverage. Please review.

Project coverage is 73.22%. Comparing base (bbc6224) to head (52abcf4).
Report is 340 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #22837      +/-   ##
============================================
- Coverage     73.57%   73.22%   -0.35%     
- Complexity    32624    32931     +307     
============================================
  Files          1877     1888      +11     
  Lines        139502   141756    +2254     
  Branches      15299    15558     +259     
============================================
+ Hits         102638   103802    +1164     
- Misses        28908    29936    +1028     
- Partials       7956     8018      +62     

Flag	Coverage Δ
inttests	27.37% <80.00%> (+2.79%)	⬆️
systests	24.74% <26.66%> (+0.42%)	⬆️
unittests	72.25% <83.33%> (-0.60%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
.../pulsar/opentelemetry/OpenTelemetryAttributes.java	100.00% <ø> (ø)
...ulsar/broker/stats/OpenTelemetryConsumerStats.java	98.36% <87.50%> (ø)
...ava/org/apache/pulsar/broker/service/Consumer.java	86.81% <81.81%> (+0.15%)	⬆️

... and 378 files with indirect coverage changes

[asafm]

Perfect @dragosvictor !