Update brand and design guidelines

[martinbonnin]

The new website brings refreshed design elements (green, gradients, stripes, ...). The Figma file has a pretty extensive design system. It would be cool to update https://graphql.org/brand/ to include those.

Additionally, putting more content to help the community would be super useful:

• social templates for locals
• slide deck
• more?

[benjie]

It would definitely be good to have these resources (e.g. for Locals); but I think the brand page relates specifically to the registered GraphQL trademark so they should probably be detailed elsewhere.

[martinbonnin]

Other examples of brand pages:

• https://gradle.com/brand/
• https://kotlinfoundation.org/guidelines/
• https://rustfoundation.org/brand-guide/

Kotlin and Rust have separate pages for "trademark policy" vs "brand guide". First one is more text, second one is more visual. If we go that road, I would vote for moving some of the info (color codes, spacing, color use) of the existing page to the brand guide, together with the new green & typefaces, etc...