docs: document default sql target schema change logic

[pnadolny13]

The sql target SDK docs should explain what the recommended behavior is for target developers and what the default behavior is for targets. Pipelinewise has there docs here https://transferwise.github.io/pipelinewise/user_guide/schema_changes.html.

• Can schema changes be disabled? I would rather get an error than let the target manipulate my tables.
• What happens if a column is added to my tap schema?
• What happens if an existing column type changes? Should it be alter?
• What if the alter is an unsupported data type change? Pipelinewise uses versioning to renames the original and creates a new column with the new type.
• What happens if a column is deleted from my tap schema?

[stale[bot]]

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[edgarrmondragon]

Still relevant