## What changes were proposed in this pull request?
Currently `HiveExternalCatalog` will filter out the Spark SQL internal table properties, e.g. `spark.sql.sources.provider`, `spark.sql.sources.schema`, etc. This is reasonable for external users as they don't want to see these internal properties in `DESC TABLE`.
However, as a Spark developer, sometimes we do wanna see the raw table properties. This PR adds a new internal SQL conf, `spark.sql.debug`, to enable debug mode and keep these raw table properties.
This config can also be used in similar places where we wanna retain debug information in the future.
## How was this patch tested?
new test in MetastoreDataSourcesSuite
Author: Wenchen Fan <wenchen@databricks.com>
Closes#15458 from cloud-fan/debug.
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