Clickhouse feature; getting columns from source; fix field name and table path

[gladkikhtutu]

Fixes:

• getting column names from query sometimes not work, so we can get it from source.yml table description
• for clickhouse join is not working so we need to point out join algorithm
• in different databases you have only schema and no database name in table path, so node.database can be empty
• count is popular word and it can be a field in initial query, so we need to use more specifit name

[cdiniz]

Hi, @gladkikhtutu Thank you for your contribution.
We'll need to set up a Clickhouse environment in our CI/CD to be able to test this.
We'll try to tackle this soon.