File extension change request

[dmytrokosiachenko]

For convenient usage in Visual Studio Code there is a suggestion from AWS to use *.json.asl file extension. Currently with *.workflow.json extension Visual Studio Code can not define it automatically correctly as ASL file.

[mbonig]

Thanks for the suggestion! I've created a PR that allows you to provide your own extension to use with a predefined extension (AWS_RECOMMENDED_JSON_EXT). Let me know what you think.