Add Swift object Symlink function

Summary
=======

This blueprint is for adding Swift object Symlink function.

Motivation
========

From swift queens release, it becomes enable to create link of object.
(https://docs.openstack.org/releasenotes/swift/queens.html)

Horizon should have this function to enhance user's convenience.

Description
=========

- This blueprint is aiming to add new row_action ``Symlink`` .
- (Maybe it is possible to implement by extending copy function)
   https://blueprints.launchpad.net/horizon/+spec/swift-object-copy-function)

UX
===
Similar to current implementation of other kind of single page angular application.
This new page should have 2 fields as follows.
- Symlink target container name input field.
- Symlink target object name input field.

Testing
======
Standard JS unit testing

Outside Dependencies
==================
N/A

Requirements Update Required
========================
N/A

Doc Impact
=========
N/A