fix: pass creds via env vars if vercel
fix vercel build https://vercel.com/elementl/dagster/CRmVHxrc72M4p3BfD8iwW3XEXeMq
the aws creds weren't correctly configured in the vercel envs. according to https://vercel.com/support/articles/how-can-i-use-aws-sdk-environment-variables-on-vercel we will need to configure it via env vars. while we still want to use aws cred profiles in other deployements (e.g. bk), this diff does the special treatment for vercel.
Test Plan: preview works: https://dagster-fia92dzji-elementl.vercel.app/getting-started
Reviewers: jordansanders, sashank
Reviewed By: jordansanders
Differential Revision: https://dagster.phacility.com/D8599