Support of ALIAS columns in Clickhouse

[igrpon]

Suggestion: implement support of ALIAS columns in Clickhouse

Background: There are ALIAS columns that could be created in Clickhouse tables, those columns are calculated columns (values) that are not stored physically, but calculated on the fly. Those columns could not be used in INSERT SQL statements
ref: https://clickhouse.com/docs/sql-reference/statements/create/table#alias

Problem: Currently in case sling replication config contains table_dll definition in target_options:

    target_options:
      table_ddl: |
        CREATE TABLE tbl (
            id UUID,
            create_ts DateTime64(6),
            is_deleted_01 Int8, -- it is Bool by nature
            is_deleted Bool ALIAS (equals(is_deleted_01, 1)),    -- this a hack as sling is not able to correctly cast PG BOOL into CH Bool
            dt Date,

with such DDL sling starts replication process, but on the final step (moving _tmp table into real one) it fails.

It fails because sling parse table_ddl and think that e.g. is_deleted column (in example above) is a real column, and it tries to insert data into it:

~ Error executing query
--- transaction.go:149 ExecMultiContext ---
~ Error executing: insert into `tbl`
                (`id`, `create_ts`, `is_deleted_01`, `is_deleted`, `dt`, 

Suggestion: enable sling to detect ALIAS columns and skip/remove them from INSERT statements

[flarco]

Created #650