Feat start time parameter on read changes

[ryanpq]

Description

Adds support for start_time parameter in read_changes

References

openfga/sdk-generator#455

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 3.46821% with 167 lines in your changes missing coverage. Please review.

Project coverage is 25.68%. Comparing base (2adebcc) to head (098facf).

Files with missing lines	Patch %	Lines
model_forbidden_response.go	0.00%	79 Missing ⚠️
model_auth_error_code.go	0.00%	45 Missing ⚠️
model_assertion.go	0.00%	42 Missing ⚠️
configuration.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
- Coverage   25.98%   25.68%   -0.30%     
==========================================
  Files         102      104       +2     
  Lines       12405    12577     +172     
==========================================
+ Hits         3223     3231       +8     
- Misses       8911     9075     +164     
  Partials      271      271              

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