chore: add automated eas schema workflow

[byCedric]

Linked issue

This adds an automated workflow to keep schemas/eas.json up to date.

Additional context

The ownership of this schema is now moved to the expo/eas-cli repository. Before merging this PR:

• [x] EAS schema should be in the expo/eas-cli repository → https://github.com/expo/eas-cli/commit/7eea81ef83e6605edf5e92ff0a59c95aea96390e
• [ ] EAS CLI should be released to create the tag including this schema

Tested workflow:

• schema-metadata, with latest, https://github.com/expo/vscode-expo/actions/runs/2796676695
• schema-metadata, with 0.56.0, https://github.com/expo/vscode-expo/actions/runs/2796683490

[github-actions[bot]]

:tada: This PR is included in version 0.8.1 :tada:

The release is available on GitHub release

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