[feat][broker]PIP-255 Part-1: Add listener interface for namespace service

[hleecs]

PIP: #19806

Motivation

Modifications

In PIP-219, we want to make the partition assignment strategy pluggable.
First, we need to add listener interface for namespace service

Verifying this change

• Make sure that the change passes the CI checks.

Documentation

• doc-not-needed

Matching PR in forked repository

[315157973]

LGTM

[codecov-commenter]

Codecov Report

Merging #20406 (5d9fe29) into master (f0e97f4) will increase coverage by 0.47%.
The diff coverage is 73.33%.

@@             Coverage Diff              @@
##             master   #20406      +/-   ##
============================================
+ Coverage     72.45%   72.92%   +0.47%     
- Complexity    31898    31904       +6     
============================================
  Files          1852     1867      +15     
  Lines        138227   138486     +259     
  Branches      15175    15202      +27     
============================================
+ Hits         100150   100989     +839     
+ Misses        30098    29489     -609     
- Partials       7979     8008      +29     

Flag	Coverage Δ
inttests	24.14% <6.66%> (-0.03%)	⬇️
systests	24.94% <6.66%> (?)
unittests	72.21% <73.33%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
...ache/pulsar/broker/namespace/NamespaceService.java	69.73% <73.33%> (-0.20%)	⬇️

... and 172 files with indirect coverage changes

[RobertIndie]

This is a feature PR and introduces a new interface. Why do we cherry-pick it to branch-3.0? @Technoboy-