Without explicitly setting the encoding to "utf-8" I get the following error on windows (python 3.9)
```
File "D:\env\lib\site-packages\graphene_django\management\commands\graphql_schema.py", line 115, in handle
self.get_schema(schema, out, indent)
File "D:\env\lib\site-packages\graphene_django\management\commands\graphql_schema.py", line 72, in get_schema
self.save_graphql_file(out, schema)
File "D:\env\lib\site-packages\graphene_django\management\commands\graphql_schema.py", line 59, in save_graphql_file
outfile.write(print_schema(schema.graphql_schema))
File "C:\Users\u\AppData\Local\Programs\Python\Python39\lib\encodings\cp1252.py", line 19, in encode
return codecs.charmap_encode(input,self.errors,encoding_table)[0]
```
* merge master into v3
* fix order_by snake casing by checking if value is None, switch executor to execution_context_class since schema.execute no longer supports executor
* fix linting by removing duplicate defintion and test of convert_form_field_to_string_list
When we use the `graphql_schema` management command, the output can vary from run to run depending on arbitrary factors (because there is no guarantee made about the order used to output JSON dictionary keys). This makes it difficult to compare two schema's at different points in time.
We address this by including a new `canonical` flag to the command, which uses standard `json.dump` funcitonality to sort dictionary keys and force pretty-printed output.
