convert plugin 'sandbox's UI to use ant.design
convert plugin 'sandbox's UI to use ant.design

Summary:
Bootcamp task:
I’m removing the remaining UI components imported from ‘flipper’ and replacing with new ones from ‘antd’.
I’m also attempting to polish 🇵🇱 the UI and UX of the plugin:

UI:
- Selecting one of the listed sandboxes and custom URL lead to the same action -> align all components together

UX:
- Sometimes loading sandboxes takes time, and it’s not clear for the user what’s happening -> add a loading indicator
- At first the input field was a bit confusing to me -> add more labels to explain the purpose of visible components
- It’s not always clear what happened after requesting a sandbox change -> the result of all actions is now confirmed with the small 'popup' notification.

I don't have any experience with web frontend, so if something is terribly wrong below - don't be afraid to point it out :)

Before/After:

{F745958473}

Reviewed By: mweststrate

Differential Revision: D37343946

fbshipit-source-id: 3dbdd213ffd5540dc7a418c1590eb956ef4c6715

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