fix: remove the gorm tag for CreatedAt and UpdatedAt

[chlins]

This pull request simplifies the BaseModel struct in manager/models/models.go by removing redundant GORM tags from the CreatedAt and UpdatedAt fields.

Code simplification:

• manager/models/models.go: Removed the gorm tags specifying column names, types, defaults, and comments for the CreatedAt and UpdatedAt fields in the BaseModel struct, leaving only the json tags.

Description

Related Issue

#3989

Motivation and Context

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[Liam-Zhao]

LGTM

[gaius-qi]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.39%. Comparing base (2d331fc) to head (290071c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3990      +/-   ##
==========================================
- Coverage   34.40%   34.39%   -0.01%     
==========================================
  Files         341      341              
  Lines       40084    40084              
==========================================
- Hits        13789    13786       -3     
- Misses      25389    25391       +2     
- Partials      906      907       +1     

Flag	Coverage Δ
unittests	34.39% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
manager/models/models.go	27.39% <ø> (ø)

... and 1 file with indirect coverage changes

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