Added Next.js example with Webhooks, Customer Portal and Checkout creation

[ronitize]

• ensure best practices with the use of env and other underlying services by the framework
• name it as with-nextjs
• use prettier as done in main /export-all-customers-to-csv
• install the latest version of Polar, shadcn/ui and Next.js
• maintain seperate API routes for each, Webhooks handler, Customer Portal handler and Checkout handler
• add an optional build-time script that validates if the access token used is valid for creating a checkout session in the relevant Polar mode (sandbox/production)
• create an installation guide like as in neondatabase/examples@ main /with-nestjs
• create the .env.example with the comments to the guides links of where the values can be obtained from
• share the deployed application to Vercel with the recording of all the 3 functionalities working

VIDEO ALSO ATTACHED

Deployed URL - https://with-nextjs-five.vercel.app/

output.mp4

[vercel]

@ronitize is attempting to deploy a commit to the polar-sh Team on Vercel.

A member of the Team first needs to authorize it.

[ronitize]

@rishi-raj-jain Can I get a review on this .

[rishi-raj-jain]

Unfortunately, I won't be able to review this since the issue is assigned to @Shivam-Batham and #9 is already in the works.

Do consider re-commenting if #9 gets closed.