Migrate `graph` commands to Zod

Part of #6807

Commands to migrate:

- [ ] `graph changelog list`
- [ ] `graph schemaextension add`
- [ ] `graph schemaextension get`
- [ ] `graph schemaextension list`
- [ ] `graph schemaextension remove`
- [ ] `graph schemaextension set`
- [ ] `graph subscription add`