Persist table comment from create table

[fulghum]

We parse table comments, but they were not persisted anywhere. This change adds support for persisting table comments so that they can be round-tripped between create table and show create table.

There are still several limitations with table comments that we should eventually follow up on:

• Table comments containing any single quotes are not supported – Vitess parses the table options, but then strips any quotes and replaces them with single quotes, then pushes all table options back into a single string that GMS parses again, using regexes to pull out charset, collation, and comment. If a table comment is double quoted and contains single quotes in the string, Vitess doesn't currently preserve enough information for us to reparse that correctly in GMS. The right fix for this is to change Vitess to return table options in a structure, instead of as a single string.
• ALTER TABLE does not support altering a table's comment.

Related to dolthub/dolt#7416

[zachmu]

LGTM