Swagger for Game Server API (#393)

* added go swag packages

* added swag and gin-swagger packages

* generated swagger docs

* added general and get game server build API definition

* corrects GameServerBuild name in summary

* dynamically set swagger host from gin context; adds api definition of listGameServers

* fixes testify package import errors

* ran go mod tidy

* added api definition for gameserver list by build name

* added api definition for get gameserver

* added api definition to delete gameserver

* added api definition to patch gameserverbuild

* added api definition to create and list game server builds

* added api definition for get gameserverdetail

* corrected api defiinitions

* corrected param names in api definitions

* updated swagger docs