Added new Divider component

[Mil4n0r]

Checklist

• Build process is done without errors. All tests pass in the /lib directory.
• Self-reviewed the code before submitting.
• Meets accessibility standards.
• Added/updated documentation to /website as needed.
• Added/updated tests as needed.

Description
A new Divider component is required based on the following design and props: https://preview.uxpin.com/c59c7c54afe8009ba5082153d70cd86fb91be7e7#/pages/165565398/simulate/no-panels

Closes #1834

[kukoc]

I suggest to quickly prepare the component api using your template and share it to have a quick review from the team devs.

[Mil4n0r]

I also added a change at SideNav to match the colors used in the rest of the dividers.

[Mil4n0r]

There is still a pending discussion regarding whether or not we will add a field to address accessibility scenarios where screen readers would want to detect the Divider if it is not only decorative but serves as a semantic separator.

It was proposed by @GomezIvann to add a new decorative field that sets aria-hidden and is set as true by default.

[Mil4n0r]

It has been decided to add the decorative prop to the component API for accessibility purposes (regarding screen readers and divider visibility).

The component is now ready to review. We have to take into account that, after the component is added, it should be integrated into the existing parts of the code that use dividers (SideNav, Contextual Menu...)