pubsub: add getAttributes for gcp pubsub

[LihaoLiuXs]

Summary

Some conventions to follow

1. add the module name as a prefix

• for example: if your change is for blob store, 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:

[codecov-commenter]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.45%. Comparing base (581005b) to head (2b8d6ee).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../multicloudj/pubsub/client/GetAttributeResult.java	83.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #109      +/-   ##
============================================
+ Coverage     78.19%   82.45%   +4.25%     
============================================
  Files           136      137       +1     
  Lines          7036     7068      +32     
  Branches        801      804       +3     
============================================
+ Hits           5502     5828     +326     
+ Misses         1112      823     -289     
+ Partials        422      417       -5     

Flag	Coverage Δ
unittests	82.45% <89.47%> (+4.25%)	⬆️

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