As a maintainer of Wikibase PHP code I want to extract a Changes package from the Wikibase monorepo and understand what are advantages and drawbacks of using git subtree command and splitsh tool

Acceptance criteria

• Changes is stored as a git repository inside of Wikibase git repository (using git subtree logic)
• Changes is published to packagist from X's readonly git repository
• Observations and challenges identified when using git subtree and splitsh/lite having been documented (free form) in this task