Bump `@keystone-6/core` to version `2.0.0`

[borisno2]

Upgrade keystone to new majors

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: a093bbbbb5e0075c8eb3ab202dceabf5eafea9fd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ------------------- | ----- | | create-keystone-app | Major |

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