MM-11120 Adding setting to disable email invitations and rate limiting. (#9063)

* Adding setting to disable email invitations.

* Adding a setting and rate limiting for email invite sending.

* Modifying email rate limit to 20/user/hour

* Adding EnableEmailInvitations to client side config and command.

app/command_invite_people.go

@@ -28,7 +28,7 @@ func (me *InvitePeopleProvider) GetTrigger() string {
 
 func (me *InvitePeopleProvider) GetCommand(a *App, T goi18n.TranslateFunc) *model.Command {
 	autoComplete := true
-	if !a.Config().EmailSettings.SendEmailNotifications || !*a.Config().TeamSettings.EnableUserCreation {
+	if !a.Config().EmailSettings.SendEmailNotifications || !*a.Config().TeamSettings.EnableUserCreation || !*a.Config().ServiceSettings.EnableEmailInvitations {
 		autoComplete = false
 	}
 	return &model.Command{
@@ -49,6 +49,10 @@ func (me *InvitePeopleProvider) DoCommand(a *App, args *model.CommandArgs, messa
 		return &model.CommandResponse{ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL, Text: args.T("api.command.invite_people.invite_off")}
 	}
 
+	if !*a.Config().ServiceSettings.EnableEmailInvitations {
+		return &model.CommandResponse{ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL, Text: args.T("api.command.invite_people.email_invitations_off")}
+	}
+
 	emailList := strings.Fields(message)
 
 	for i := len(emailList) - 1; i >= 0; i-- {