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

app/session.go

@@ -362,7 +362,7 @@ func (a *App) CreateUserAccessToken(token *model.UserAccessToken) (*model.UserAc
 
 	// Don't send emails to bot users.
 	if !user.IsBot {
-		if err := a.Srv().EmailService.sendUserAccessTokenAddedEmail(user.Email, user.Locale, a.GetSiteURL()); err != nil {
+		if err := a.Srv().EmailService.SendUserAccessTokenAddedEmail(user.Email, user.Locale, a.GetSiteURL()); err != nil {
 			a.Log().Error("Unable to send user access token added email", mlog.Err(err), mlog.String("user_id", user.Id))
 		}
 	}