Introduce DatabaseMigrations custom resource definition (CRD)

What does this MR do?

Introduce DatabaseMigrations custom resource definition (CRD)

The Databasemigrations custom resource can be used to upgrade a rails database.

This only add the CRD and it's validation. The controller will be implemented in #104 (closed).

Closes #103 (closed)

Closes #105 (closed)

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Related issues