[bug] edge server function monorepo environment variable

[lucasvieirasilva]

Issue

When the Next.js project is created using a monorepo structure and deployed using the SST NextjsSite construct, the server function fails when the region where the user is located is different from the S3 cache bucket.

PermanentRedirect: The bucket you are attempting to access must be addressed using the specified endpoint. Please send all future requests to this endpoint.

Cause

When OpenNext identifies a monorepo structure, it calls the addMonorepoEntrypoint function and creates a index.js exporting the handler inside the project package:

Source reference:
addMonorepoEntrypoint](https://github.com/sst/open-next/blob/3a5755fdcbfdf688cedc355e892b5ed74787993f/packages/open-next/src/build.ts#L712-L725)

SST adds the following code before the export * and the final code looks like:

process.env = { ...process.env, ..."{{ _SST_FUNCTION_ENVIRONMENT_ }}" };
export * from "./apps/frontend/admin-ui/index.mjs";

However, the way node.js works the imports run before the process.env block, the CACHE_BUCKET_REGION is not defined and the S3Client is defined without the right region:

https://github.com/sst/open-next/blob/3a5755fdcbfdf688cedc355e892b5ed74787993f/packages/open-next/src/adapters/server-adapter.ts#L33-L37