wip: Extend VSchema DDL to add/drop columns

[davidpiegza]

Description

Related Issue(s)

• Feature Request: Add VSchema DDL support to add/drop columns and alter table options #14078

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

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[github-actions]

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If no action is taken within 7 days, this PR will be closed.

[github-actions]

This PR was closed because it has been stale for 7 days with no activity.