Add note to UPGRADE guide for change in Validator behavior

[particleflux]

The unique and exists validators behave slightly different since 2.0.46 (issue #19407) when used on multiple/combined attributes.

This adds a note about it in the UPGRADE guide

See: #19407 (comment)

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌
Fixed issues

[what-the-diff]

PR Summary

• Update to Validation Error Reporting
  Previously, the UniqueValidator and ExistValidator in our code would generate separate errors for each attribute processed. Now, they will generate a single error even when used across multiple attributes. This can make identifying and resolving issues simpler and cleaner. However, if you preferred the old system, you can revert back by setting 'skipOnError' => false. Do note that this might cause unintended complications with additional validators on one of the target attributes. More details on this matter can be found in issue #19407.

• Deprecation of 'rotateByCopy' Function In File Logging
  The rotateByCopy function in our file logging has been marked as deprecated and setting it to false will not affect the system. This change will streamline our logging process since henceforth files will be rotated only by copying. This uniform method should eliminate any inconsistencies and potential error points.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (4c0a00f) 48.91% compared to head (2c91716) 48.91%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #19938   +/-   ##
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  Coverage   48.91%   48.91%           
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  Files         445      445           
  Lines       42810    42810           
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  Hits        20941    20941           
  Misses      21869    21869           

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[samdark]

Thank you!

[schmunk42]

when used on multiple attributes, now only generate an error on a single attribute. Previously, they would report a separate error on each attribute.

@samdark @bizley @particleflux @xcopy Which attribute is picked for the error?

[particleflux]

@schmunk42 In my case, it was the last one specified, though I'm not sure if that is always the case.

The errors on this comment is exactly what our test suite catched: it used to report both in order they were defined, but with newer version it only reported the last one only.

[bizley]

IIRC all attributes considered valid are picked.