[cherry-pick] Breaking change: Rename Stage to Volume

[lentitude2tk]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 98.36066% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@afff26c). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pymilvus/bulk_writer/volume_file_manager.py	96.77%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3112   +/-   ##
=========================================
  Coverage          ?   46.34%           
=========================================
  Files             ?       66           
  Lines             ?    13874           
  Branches          ?        0           
=========================================
  Hits              ?     6430           
  Misses            ?     7444           
  Partials          ?        0           

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[XuanYang-cn]

/lgtm

[sre-ci-robot]

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