feat(clickhouse): support generate TimestampTrunc, Variance, Stddev

[longxiaofei]

References:

• https://clickhouse.com/docs/en/sql-reference/functions/date-time-functions#date_trunc
• https://clickhouse.com/docs/en/sql-reference/aggregate-functions/reference/varsamp
• https://clickhouse.com/docs/en/sql-reference/aggregate-functions/reference/stddevsamp