__dbt_backup relation dropped on cluster for dictionaries (fixes #325)

[the4thamigo-uk]

Summary

fixes #325

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials