chores: add examples to illustrate pubsub in Main.java class

[Yaminik1996]

Summary

< Provide a brief description of the changes in this PR >

Some conventions to follow

1. add the module name as a prefix
   • for example: add a prefix: docstore: for document store module, blobstore for Blob Store module
2. for a test only PR, add test:
3. for a perf improvement only PR, add perf:
4. for a refactoring only PR, add "refactor:"

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.59%. Comparing base (627b53c) to head (1a77aaf).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #181      +/-   ##
============================================
- Coverage     83.63%   83.59%   -0.04%     
  Complexity       90       90              
============================================
  Files           150      150              
  Lines          8041     8046       +5     
  Branches        940      942       +2     
============================================
+ Hits           6725     6726       +1     
- Misses          873      875       +2     
- Partials        443      445       +2     

Flag	Coverage Δ
unittests	83.59% <ø> (-0.04%)	⬇️

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