Decouple emailservice from app package (#17827)

* decouple emailservice from app package

* fix some escaped errors

* move email package under app directory

* fix i18n

* reflect review comments

api4/cloud.go

@@ -435,8 +435,8 @@ func handleCWSWebhook(c *Context, w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
-		if appErr := c.App.Srv().EmailService.SendCloudWelcomeEmail(user.Email, user.Locale, team.InviteId, subscription.GetWorkSpaceNameFromDNS(), subscription.DNS, *c.App.Config().ServiceSettings.SiteURL); appErr != nil {
-			c.Err = appErr
+		if err := c.App.Srv().EmailService.SendCloudWelcomeEmail(user.Email, user.Locale, team.InviteId, subscription.GetWorkSpaceNameFromDNS(), subscription.DNS, *c.App.Config().ServiceSettings.SiteURL); err != nil {
+			c.Err = model.NewAppError("SendCloudWelcomeEmail", "api.user.send_cloud_welcome_email.error", nil, err.Error(), http.StatusInternalServerError)
 			return
 		}
 	case model.EventTypeTrialWillEnd: