feat: support start_time parameter on read_changes

[ryanpq]

Description

Adds support for the start_time variable for 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

[ryanpq]

Note: This currently includes the read changes start_time variable but does not include Batch Check updates.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 87.65%. Comparing base (81ab8be) to head (cda05b4).

Files with missing lines	Patch %	Lines
api.ts	66.66%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #186      +/-   ##
==========================================
- Coverage   87.70%   87.65%   -0.06%     
==========================================
  Files          23       23              
  Lines        1139     1142       +3     
  Branches      177      179       +2     
==========================================
+ Hits          999     1001       +2     
  Misses         83       83              
- Partials       57       58       +1     

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