Return Router interface from controller constructor. (#4196)

Update the go server api controller template to return the Router interface instead of the api specific router.
The Router interface type has the Routes function, which is what the generated `NewRouter` function needs. (not the api specific interface).

modules/openapi-generator/src/main/resources/go-server/controller-api.mustache

@@ -15,7 +15,7 @@ type {{classname}}Controller struct {
 }
 
 // New{{classname}}Controller creates a default api controller
-func New{{classname}}Controller(s {{classname}}Servicer) {{classname}}Router {
+func New{{classname}}Controller(s {{classname}}Servicer) Router {
 	return &{{classname}}Controller{ service: s }
 }
 

samples/server/petstore/go-api-server/go/api_pet.go

@@ -23,7 +23,7 @@ type PetApiController struct {
 }
 
 // NewPetApiController creates a default api controller
-func NewPetApiController(s PetApiServicer) PetApiRouter {
+func NewPetApiController(s PetApiServicer) Router {
 	return &PetApiController{ service: s }
 }
 

samples/server/petstore/go-api-server/go/api_store.go

@@ -23,7 +23,7 @@ type StoreApiController struct {
 }
 
 // NewStoreApiController creates a default api controller
-func NewStoreApiController(s StoreApiServicer) StoreApiRouter {
+func NewStoreApiController(s StoreApiServicer) Router {
 	return &StoreApiController{ service: s }
 }
 

samples/server/petstore/go-api-server/go/api_user.go

@@ -23,7 +23,7 @@ type UserApiController struct {
 }
 
 // NewUserApiController creates a default api controller
-func NewUserApiController(s UserApiServicer) UserApiRouter {
+func NewUserApiController(s UserApiServicer) Router {
 	return &UserApiController{ service: s }
 }