[OUDS] docs : add "Guidelines" page

[vprothais]

Prerequisites

• [x] I have searched for duplicate or closed feature requests
• [x] I have read the contributing guidelines

Proposal

Adds the "Guidelines" page based on:

• the previous corresponding Boosted page (see code source)

Motivation and context

Sub task of https://github.com/Orange-OpenSource/Orange-Boosted-Bootstrap/issues/2589

[B3nz01d]

This page needs to be clarified as the previous design guidelines in the DSM where platform specific and it is not the cas anymore. The main redirection should be to the OUDS DSM: https://unified-design-system.orange.com/ We could also highlight the following informations:

• Tokens: https://unified-design-system.orange.com/472794e18/p/36c0be-design-tokens
• Components: https://unified-design-system.orange.com/472794e18/p/73c701-components

Also links that could be added are the links to the other platforms dev doc. I'm not sure they fit in this page or in a new tab to gather around "Dev platforms" or in a section in this page, and maybe @Franco-Riccitelli could help set this up. The links should include:

• Android: https://android.unified-design-system.orange.com
• iOS: https://ios.unified-design-system.orange.com
• Flutter: https://flutter.unified-design-system.orange.com