ARROW-7889: [Rust] Add support to datafusion-cli for parquet files.

At present, using datafusion-cli with a parquet file results in an error that Parquet is unsupported.

This change allows the registration of parquet files with `CREATE EXTERNAL TABLE`.

Closes #6456 from maxburke/parquet_datafusion_cli and squashes the following commits:

5aad806 <Max Burke> cargo fmt
138717c <Max Burke> Add support to datafusion-cli for parquet files.

Authored-by: Max Burke <max@urbanlogiq.com>
Signed-off-by: Krisztián Szűcs <szucs.krisztian@gmail.com>

rust/datafusion/src/execution/context.rs

@@ -93,6 +93,10 @@ impl ExecutionContext {
                     self.register_csv(name, location, schema, *header_row);
                     Ok(vec![])
                 }
+                FileType::Parquet => {
+                    self.register_parquet(name, location)?;
+                    Ok(vec![])
+                }
                 _ => Err(ExecutionError::ExecutionError(format!(
                     "Unsupported file type {:?}.",
                     file_type