Implement APIv4 infrastructure (#5191)

* Implement APIv4 infrastructure

* Update parameter requirement functions per feedback

cmd/platform/server.go

@@ -16,6 +16,7 @@ import (
 
 	l4g "github.com/alecthomas/log4go"
 	"github.com/mattermost/platform/api"
+	"github.com/mattermost/platform/api4"
 	"github.com/mattermost/platform/app"
 	"github.com/mattermost/platform/einterfaces"
 	"github.com/mattermost/platform/manualtesting"
@@ -73,6 +74,7 @@ func runServer(configFileLocation string) {
 	app.NewServer()
 	app.InitStores()
 	api.InitRouter()
+	api4.InitApi(false)
 	api.InitApi()
 	web.InitWeb()