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ARROW-9656: [Rust] [DataFusion] Better error messages for unsupported EXTERNAL TABLE types

Previously, the error message for an invalid CREATE EXTERNAL TABLE command told the user there was a problem but not how to fix it. This PR improves the error message and adds some parser tests.

Before this PR:

```
CREATE EXTERNAL TABLE repro
STORED AS ARROW
LOCATION 'repro.arrow';

ParserError(ParserError("Expected fileformat, found: ARROW"))
```

After this PR:
```
CREATE EXTERNAL TABLE repro
STORED AS ARROW
LOCATION 'repro.arrow';

ParserError(ParserError("Expected one of PARQUET, NDJSON, or CSV, found: ARROW"))
```

Closes #7905 from alamb/alamb/better-parser-errors

Authored-by: alamb <andrew@nerdnetworks.org>
Signed-off-by: Andy Grove <andygrove@nvidia.com>