message: docs(athena): add assuming IAM role with PyAthena
diff: @@ -32,3 +32,11 @@ following connection string:
  ```
  awsathena+rest://{aws_access_key_id}:{aws_secret_access_key}@athena.{region_name}.amazonaws.com/{schema_name}?s3_staging_dir={s3_staging_dir}&...
  ```
  +
  +The PyAthena library also allows to assume a specific IAM role, by [importing the datasource from YAML](https://superset.apache.org/docs/miscellaneous/importing-exporting-datasources/#importing-datasources-from-yaml) and passing extra parameters:
  +```
  +databases:
  + - database_name: awsathena
  + sqlalchemy_uri: awsathena+rest://athena.{region_name}.amazonaws.com/{schema_name}?s3_staging_dir={s3_staging_dir}&...
  + extra: "{\"engine_params\": {\"connect_args\": {\"role_arn\": \"{{ ROLE_ARN }}\" }}}"
  +```
  