[SPARK-34359][SQL][3.1] Add a legacy config to restore the output schema of SHOW DATABASES #31486
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This backports #31474 to 3.1/3.0
What changes were proposed in this pull request?
This is a followup of #26006
In #26006 , we merged the v1 and v2 SHOW DATABASES/NAMESPACES commands, but we missed a behavior change that the output schema of SHOW DATABASES becomes different.
This PR adds a legacy config to restore the old schema, with a migration guide item to mention this behavior change.
Why are the changes needed?
Improve backward compatibility
Does this PR introduce any user-facing change?
No (the legacy config is false by default)
How was this patch tested?
a new test