feat: delete custom user attributes from subsequent events

[zhu-xiaowei]

Description

1. delete custom user attributes from subsequent events

NOTE: This is a breaking change, only pipelines from version 1.1+ can handle events without custom user attribute.

General Checklist

• Added new tests to cover change, if needed
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3ec2af3) 100.00% compared to head (31ac7b7) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #36   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           24        24           
  Lines          996      1006   +10     
  Branches       183       186    +3     
=========================================
+ Hits           996      1006   +10     

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