[Website] Add pricing page

[Romakita]

Goal

To improve the sponsors engagement, we need to add a page that display the different tiers. Ts.ED stay free and open-source. The main idea is to push premium offers like "dedicated channel for company" etc...

Rules:

• This page must be display when a user click on the slack link.

It let the developers to choose a tiers:

• The free tiers redirect the user to the slack (maybe a delay before enable button can be added)
• The others tiers redirect the user to github sponsors

[Romakita]

The page is almost ready and need to be rebased / fixed.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.