Provide new component Flex

[ahmehri]

Is your feature request related to a problem? Please describe.

Context: #557 (comment)

My use case is positioning two items vertically with a container that has a fixed height, and position them in a way that there is a space between them.

This is not possible to implement right now with ui-kit components.

Describe the solution you'd like

A new component Flex (similar to the existing component Grid) can solve the problem here.

Describe alternatives you've considered

Using the component Spacings.Stack should solve the problem, except the CSS property justify-content is not supported. It turned out that even if it was supported, the problem won't be solved because the container needs to have a fixed height (which means a new prop height should be added too).

This is not a good idea after all because spacing components are not the same as Flexbox containers. Yes, they internally use Flexbox but they aim to solve a specific use case.