MM-12849 Moving all non request scoped items to Server struct (#9806)

* Moving goroutine pool

* Auto refactor

* Moving plugins.

* Auto refactor

* Moving fields to server

* Auto refactor

* Removing siteurl duplication.

* Moving reset of app fields

* Auto refactor

* Formatting

* Moving niling of Server to after last use

* Fixing unit tests.

app/file.go

@@ -444,7 +444,7 @@ func (a *App) DoUploadFileExpectModification(now time.Time, rawTeamId string, ra
 	if a.PluginsReady() {
 		var rejectionError *model.AppError
 		pluginContext := &plugin.Context{}
-		a.Plugins.RunMultiPluginHook(func(hooks plugin.Hooks) bool {
+		a.Srv.Plugins.RunMultiPluginHook(func(hooks plugin.Hooks) bool {
 			var newBytes bytes.Buffer
 			replacementInfo, rejectionReason := hooks.FileWillBeUploaded(pluginContext, info, bytes.NewReader(data), &newBytes)
 			if rejectionReason != "" {