WIP: Store changes filter by start time

[cikasfm]

Store changes filter by start time

Description

Added optional start_time attribute to /store/{id}/changes API to allow streaming starting the given time stamp.

References

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

[linux-foundation-easycla[bot]]

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• :white_check_mark: login: cikasfm / name: Zilvinas Vilutis (bf8e92bcc45a0582433768c9bdc574a17c177c95, cc1ceda13f65a2bcbfa268ee5c45f85d7a10ef26, ebd592f61a25cc9f40f56feef7124ff7f603515e)