[improve] [broker] Make exposing topic level metric dynamic

[hangc0276]

Fixes #xyz

Main Issue: #xyz

PIP: #xyz

Motivation

Exposing topic-level metrics costs a lot of CPU and memory for brokers and put heavy traffic pressure on Prometheus to pull metrics, especially when the Pulsar cluster has thousands of topics. To address this issue, we can disable the topic-level metrics by default and enable it when some topics encountered any issues.

However, the exposeTopicLevelMetricsInPrometheus flag is not dynamic and we need to change the broker configuration and restart all the brokers to enable or disable the flag.

We can make the exposeTopicLevelMetricsInPrometheus flag dynamic to avoid restarting all the brokers when enabling or disabling the flag

Modifications

Make the following flags dynamic

• exposeTopicLevelMetricsInPrometheus
• exposeConsumerLevelMetricsInPrometheus
• exposeProducerLevelMetricsInPrometheus
• exposeManagedLedgerMetricsInPrometheus
• exposeManagedCursorMetricsInPrometheus
• exposePreciseBacklogInPrometheus
• exposeSubscriptionBacklogSizeInPrometheus

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

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

If the box was checked, please highlight the changes

• 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
• Anything that affects deployment

Documentation

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

Matching PR in forked repository

PR in forked repository:

[hangc0276]

@asafm Please help take a look this at this PR and it is related to metrics, thanks.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.28%. Comparing base (d6734b7) to head (7369f7f).
Report is 518 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #21006       +/-   ##
=============================================
+ Coverage     36.84%   67.28%   +30.43%     
- Complexity    12195    35854    +23659     
=============================================
  Files          1698     1921      +223     
  Lines        129852   175600    +45748     
  Branches      14161    23035     +8874     
=============================================
+ Hits          47843   118148    +70305     
+ Misses        75680    47827    -27853     
- Partials       6329     9625     +3296     

Flag	Coverage Δ
inttests	24.27% <28.57%> (+0.14%)	⬆️
systests	27.51% <50.00%> (+2.42%)	⬆️
unittests	66.47% <100.00%> (+34.40%)	⬆️

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

Files	Coverage Δ
...org/apache/pulsar/broker/ServiceConfiguration.java	98.09% <100.00%> (+0.04%)	⬆️
...n/java/org/apache/pulsar/broker/PulsarService.java	81.49% <100.00%> (+12.93%)	⬆️
...ats/prometheus/PulsarPrometheusMetricsServlet.java	100.00% <100.00%> (+22.22%)	⬆️

... and 1508 files with indirect coverage changes

[asafm]

@hangc0276 It looks ok, aside from the fact that you don't have any test to validate it and protect from even being ruined :)

[github-actions]

The pr had no activity for 30 days, mark with Stale label.

[dao-jun]

LGTM