[improve][broker] Improve NamespaceUnloadStrategy error message

[dragosvictor]

Motivation

The log message printed when failing to create the NamespaceUnloadStrategy class instance mistakenly references a different config option.
Additionally fixes setup for tests in ProxyWithExtensibleLoadManagerTest, where the option was defaulting to value org.apache.pulsar.broker.loadbalance.impl.ThresholdShedder, which is incompatible with the extensible load manager, and was producing the following error message during test runs:

2024-01-10T14:57:28,347 - ERROR - [main:UnloadScheduler@222] - Error when trying to create namespace unload strategy: org.apache.pul
sar.broker.loadbalance.impl.LeastLongTermMessageRate
java.lang.RuntimeException: org.apache.pulsar.broker.loadbalance.impl.ThresholdShedder does not implement org.apache.pulsar.broker.l
oadbalance.extensions.scheduler.NamespaceUnloadStrategy
        at org.apache.pulsar.common.util.Reflections.createInstance(Reflections.java:75) ~[pulsar-common-3.3.0-SNAPSHOT.jar:3.3.0-SN
APSHOT]
        at org.apache.pulsar.broker.loadbalance.extensions.scheduler.UnloadScheduler.createNamespaceUnloadStrategy(UnloadScheduler.j
ava:217) ~[pulsar-broker-3.3.0-SNAPSHOT.jar:3.3.0-SNAPSHOT]

Modifications

Alter the log message in org.apache.pulsar.broker.loadbalance.extensions.scheduler.UnloadScheduler#createNamespaceUnloadStrategy to properly reference config option loadBalancerLoadSheddingStrategy.
Set loadBalancerLoadSheddingStrategy to org.apache.pulsar.broker.loadbalance.extensions.scheduler.TransferShedder in ProxyWithExtensibleLoadManagerTest#configureExtensibleLoadManager.

Verifying this change

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

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• 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

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Matching PR in forked repository

PR in forked repository: https://github.com/dragosvictor/pulsar/pull/8/files

[github-actions]

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (46ec730) 73.54% compared to head (69f619e) 73.55%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #21880      +/-   ##
============================================
+ Coverage     73.54%   73.55%   +0.01%     
- Complexity    32311    32327      +16     
============================================
  Files          1859     1859              
  Lines        138281   138280       -1     
  Branches      15156    15156              
============================================
+ Hits         101693   101716      +23     
+ Misses        28689    28677      -12     
+ Partials       7899     7887      -12     

Flag	Coverage Δ
inttests	24.14% <0.00%> (-0.02%)	⬇️
systests	23.67% <0.00%> (-0.07%)	⬇️
unittests	72.84% <100.00%> (+0.02%)	⬆️

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

Files	Coverage Δ
...dbalance/extensions/scheduler/UnloadScheduler.java	85.43% <100.00%> (-0.15%)	⬇️

... and 59 files with indirect coverage changes