Add simple swagger/redoc api documentation

[kconde2]

• https://medium.com/@sushildamdhere/how-to-document-rest-apis-with-swagger-and-ruby-on-rails-ae4e13177f5d

• https://devhub.io/zh/repos/krsyoung-redoc-rails

[kconde2]

https://github.com/domaindrivendev/rswag