This adds a new example under `cms-plasmic/`. It serves as a general-purpose example that should be able to work with any Plasmic project, which can be set via environment variables.
## Documentation / Examples
- [x] Make sure the linting passes by running `pnpm lint`
- [x] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
