allows to add a comment in table's or view's metadata

[dstsimokha]

Summary

closes #227 Now the comment from the config is added to Clickhouse materialization metadata, that's all (probably that's the smallest commit possible)

[CLAassistant]

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[BentsiLeviav]

Hi @dstsimokha

Thank you so much for your contribution. Could you please resolve the conflicts in your branch?

[simpl1g]

@BentsiLeviav there is persist_docs macro that already adds comment to table and columns, I guess this PR should be reverted