[New Generator] Lisp client generator

Description

We would like to create a Lisp client generator so that Lisp 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 Lisp client generator.

• create Lisp petstore samples (implemented at least 2 endpoints to start with: getPetById, addPet)
• create the templates and eng
• test the auto-generated Lisp code and revise the Lisp generator, templates

cc @incjung

openapi-generator version

Latest master

Suggest a fix/enhancement

If anyone wants to help on this (e.g. testing, creating templates, etc), please reply to let us know.