Update design of SingletonCard component, rename to Toast

[edmundito]

The SingletonCard is the component that is used to show the notification at the bottom of the screen but it needs a design refresh. Once the design is ready, this component should be updated. This component is also commonly known in other design systems as Toast, so it should be renamed.

TODO

• Design

[octavia-squidington-iii]

cc @airbytehq/frontend

[Upmitt]

@edmundito - here is a first design for the toast messages (only text messages, no action) - https://www.figma.com/file/gMNRYVJav25pdsoxAyW7Qp/00_01_WEB-APP-LIBRARIES?node-id=1475%3A2667

[edmundito]

Replaced by #18631