AI Gateway [2.0]: Create a Vercel AI provider

[jbaross]

Jobs to be done (optional)

Follows https://konghq.atlassian.net/browse/AG-126?atlOrigin=eyJpIjoiZDY5NmI2OTNiYzY1NDVjMWJlOGEyODFiMWMzOGM5NTMiLCJwIjoiaiJ9

Definition of done

• Yaml spec for autogenerated pages []
• Provider subpage [x]
• Add to list of providers with appropriate icon [x]
• Add configuration examples (this may change based on AIGW fork from GW) [~]

PR

#5373