chore: Workflow to Sync Platform Subtree on Pushes to Main (#734)

## Summary

Create workflow to trigger platform subtree pull reusable workflow.

Also deletes Push To Canary workflow as it will be triggered in the
platform repo.

## Checklist
- [ ] Added Unit Tests
- [ ] Covered by existing CI
- [ ] Integration tested
- [ ] Documentation update



<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit

- **Chores**
- Added a new workflow to automate triggering subtree updates in an
external platform repository when changes are pushed to the main branch.
- Removed the "Push To Canary" workflow, discontinuing automated
artifact builds, canary deployments, integration tests, and related
notifications for the main branch.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: chewy-zlai