[improve][broker] PIP-192 Implemented ExtensibleLoadManagerWrapper.getLoadBalancingMetrics()

[heesung-sn]

Master Issue: #16691

Motivation

We will start raising PRs to implement PIP-192, #16691

Modifications

This PR implemented ExtensibleLoadManagerWrapper.getLoadBalancingMetrics()and its unit test.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• *Added unit tests.

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
• Anything that affects deployment

Documentation

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

We will have separate PRs to update the Doc later.

Matching PR in forked repository

PR in forked repository: heesung-sn#28

[codecov-commenter]

Codecov Report

Merging #19440 (624ccd7) into master (aa7af10) will increase coverage by 0.13%.
The diff coverage is 4.86%.

@@             Coverage Diff              @@
##             master   #19440      +/-   ##
============================================
+ Coverage     64.20%   64.34%   +0.13%     
- Complexity    26265    26409     +144     
============================================
  Files          1832     1836       +4     
  Lines        134067   134570     +503     
  Branches      14753    14816      +63     
============================================
+ Hits          86077    86583     +506     
- Misses        40135    40156      +21     
+ Partials       7855     7831      -24     

Flag	Coverage Δ
inttests	24.85% <0.81%> (-0.07%)	⬇️
systests	25.48% <1.08%> (+<0.01%)	⬆️
unittests	61.62% <4.86%> (+0.16%)	⬆️

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

Impacted Files	Coverage Δ
...dbalance/extensions/ExtensibleLoadManagerImpl.java	5.88% <0.00%> (-1.60%)	⬇️
...lance/extensions/ExtensibleLoadManagerWrapper.java	0.00% <0.00%> (ø)
...xtensions/channel/ServiceUnitStateChannelImpl.java	0.73% <0.00%> (-0.24%)	⬇️
...er/loadbalance/extensions/data/BrokerLoadData.java	0.00% <0.00%> (ø)
...r/loadbalance/extensions/models/AssignCounter.java	0.00% <0.00%> (ø)
...er/loadbalance/extensions/models/SplitCounter.java	0.00% <0.00%> (ø)
...r/loadbalance/extensions/models/SplitDecision.java	0.00% <0.00%> (ø)
...r/loadbalance/extensions/models/UnloadCounter.java	0.00% <0.00%> (ø)
.../loadbalance/extensions/models/UnloadDecision.java	0.00% <ø> (ø)
...rg/apache/pulsar/broker/service/BrokerService.java	60.59% <0.00%> (+0.21%)	⬆️
... and 132 more

[Technoboy-]

LGTM