feat: add column comment

[yassun7010]

resolves #9198

Problem

In migration to dbt, we use dbt-osmosis.
I would like to retrieve comment information for a column in schema.yml from an existing table, but the current dbt-core does not have column comment field.

Solution

Add optional comment field to Column.
In existing usage, the comment is simply set to None.

I have confirmed from the column class definition information for several database adapters that adding comment information does not break backward compatibility.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

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[yassun7010]

@aranke

Is there anything I should do to promote this PR?

I look forward to your comments ;)

See also dbt-osmosis feature suggestions. z3z1ma/dbt-osmosis#120

[dbeatty10]

Similarly to #9198 and dbt-labs/dbt-codegen#119, closing this per #9198 (comment).