fix: invalidate caches for menu items

[jasonbahl]

This adds event listeners for when menu items are created, updated and deleted to purge associated caches in response to said events.

• [x] failing tests: https://github.com/wp-graphql/wp-graphql-smart-cache/actions/runs/7893082730
• [x] passing tests: https://github.com/wp-graphql/wp-graphql-smart-cache/actions/runs/7893092393

closes #260