[New Generator] Reason ML client generator

Description

We would like to create a Reason ML client generator so that Reason ML developers can find it more easily to consume REST APIs.

Similar to how some other generators (e.g. R, Lua, PowerShell) are created, we will use the reverse engineering process to create the Reason ML client generator.

• create ReasonML pet store samples (implemented at least 2 endpoints to start with: getPetById, addPet)
• reverse engineer the templates and the generator (Java class)
• test the auto-generated Reason ML code and revise the generator, templates

openapi-generator version

Latest master

Suggest a fix/enhancement

If anyone wants to work on this, please reply to let us know.