arrow

ARROW-12108: [Rust] [DataFusion] Implement SHOW TABLES

# Rationale
Accessing the list of tables via `select * from information_schema.tables` (introduced in https://github.com/apache/arrow/pull/9818) is a lot to type

See the doc for background: https://docs.google.com/document/d/12cpZUSNPqVH9Z0BBx6O8REu7TFqL-NPPAYCUPpDls1k/edit#

# Proposal

Add support for `SHOW TABLES` command.

# Commentary

This is different than both postgres (which uses `\d` in `psql` for this purpose), and MySQL (which uses `DESCRIBE`).

I could be convinced that we should not add `SHOW TABLES` at all (and just stay with `select * from information_schema.tables` but I wanted to add the proposal)

# Example Use

Setup:
```
echo "1,Foo,44.9" > /tmp/table.csv
echo "2,Bar,22.1" >> /tmp/table.csv
cargo run --bin datafusion-cli
```

Then run :

```
CREATE EXTERNAL TABLE t(a int, b varchar, c float)
STORED AS CSV
LOCATION '/tmp/table.csv';

> show tables;
+---------------+--------------------+------------+------------+
| table_catalog | table_schema       | table_name | table_type |
+---------------+--------------------+------------+------------+
| datafusion    | public             | t          | BASE TABLE |
| datafusion    | information_schema | tables     | VIEW       |
+---------------+--------------------+------------+------------+
2 row in set. Query took 0 seconds.

```

Closes #9847 from alamb/alamb/really_show_tables

Authored-by: Andrew Lamb <andrew@nerdnetworks.org>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>