Go gin driver

Created by: aronluigi

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
• Filed the PR against the correct branch: master, 4.1.x, 5.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

Motivation

I was trying to integrate the generated code from go-gin-server into a project that is using Ports & Adapters pattern. The current go-gin-server implementation didn't fit the project requirements so I needed to create a new generator that will create a driver that respects the design pattern of the project.

Features

• basic payload validations
• response type validation (make sure that the response respects the OAS3 definition)
• OAS documentation (using ReDoc)

The current implementation can handle JSON & XML responses.

TODO

• support custom validators for payload
• support different response types