Support struct field for BulkWriter

[yhmo]

issue: #3050

[codecov]

Codecov Report

❌ Patch coverage is 27.90698% with 62 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@afa03fb). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pymilvus/bulk_writer/bulk_writer.py	34.14%	27 Missing ⚠️
pymilvus/bulk_writer/buffer.py	21.21%	26 Missing ⚠️
pymilvus/bulk_writer/validators.py	11.11%	8 Missing ⚠️
pymilvus/orm/schema.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3057   +/-   ##
=========================================
  Coverage          ?   45.12%           
=========================================
  Files             ?       65           
  Lines             ?    13800           
  Branches          ?        0           
=========================================
  Hits              ?     6227           
  Misses            ?     7573           
  Partials          ?        0           

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[SpadeA-Tang]

/lgtm

[XuanYang-cn]

/approve

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: XuanYang-cn, yhmo

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