Amplify Next.js config

amplify.yml

version: 1
frontend:
  phases:
    preBuild:
      commands:
        - yarn install --frozen-lockfile
    build:
      commands:
        - yarn build
  artifacts:
    baseDirectory: .next
    files:
      - '**/*'
  cache:
    paths:
      - node_modules/**/*
      - .next/cache/**/*