## What changes were proposed in this pull request?

In https://github.com/apache/spark/pull/16296 , we reached a consensus that we should hide the external/managed table concept to users and only expose custom table path.

This PR renames `Catalog.createExternalTable` to `createTable`(still keep the old versions for backward compatibility), and only set the table type to EXTERNAL if `path` is specified in options.

## How was this patch tested?

new tests in `CatalogSuite`

Author: Wenchen Fan <wenchen@databricks.com>

Closes #16528 from cloud-fan/create-table.