Fix clickhouse schema dump with non-default database

[Flamefork]

This fixes the issue of using a generated schema.sql with ClickHouse in Docker.
The ClickHouse entrypoint runs every .sql file in /docker-entrypoint-initdb.d during server startup, but it executes them against the default database.

It works if the schema dump was created from the default database, but it fails otherwise:

/entrypoint.sh: running /docker-entrypoint-initdb.d/schema.sql
Received exception from server (version 25.3.6):
Code: 60. DB::Exception: Received from 127.0.0.1:9000. DB::Exception: Table default.schema_migrations does not exist. Maybe you meant my_database_name.schema_migrations?. (UNKNOWN_TABLE)

This fix prefixes migrations_table_name with db_name. in the generated schema, making it consistent with the table creation statements and with other drivers.