Provide an esm build for `@next/env`

### Link to the code that reproduces this issue https://github.com/AhmedBaset/next-env-repro-esm ### To Reproduce 1. Run `node script.js` 2. Run `node script.mjs` ### Current vs. Expected behavior `@next/env` doesn't work correctly with esm. This cjs works as expected ```js require("@next/env").loadEnvConfig(process.cwd()); console.log(process.env.TEST); ``` But this doesn't ```js import { loadEnvConfig } from "@next/env"; loadEnvConfig(process.cwd()); console.log(process.env.TEST); ``` It throws: ```bash import { loadEnvConfig } from "@next/env"; ^^^^^^^^^^^^^ SyntaxError: Named export 'loadEnvConfig' not found. The requested module '@next/env' is a CommonJS module, which may not support all module.exports as named exports. CommonJS modules can always be imported via the default export, for example using: import pkg from '@next/env'; const { loadEnvConfig } = pkg; ``` Let's try both cjs and esm in REPL ```bash Welcome to Node.js v20.12.2. Type ".help" for more information. > require("@next/env") Object [Module] { initialEnv: [Getter], updateInitialEnv: [Getter], processEnv: [Getter], resetEnv: [Getter], loadEnvConfig: [Getter] } > require("@next/env").default undefined > await import("@next/env") [Module: null prototype] { default: Object [Module] { initialEnv: [Getter], updateInitialEnv: [Getter], processEnv: [Getter], resetEnv: [Getter], loadEnvConfig: [Getter] } } ``` ### Provide environment information ```bash Operating System: Platform: win32 Arch: x64 Version: Windows 11 Home Single Language Available memory (MB): 15774 Available CPU cores: 12 Binaries: Node: 20.12.2 npm: N/A Yarn: N/A pnpm: N/A Relevant Packages: next: 14.2.4 // There is a newer version (14.2.5) available, upgrade recommended! eslint-config-next: N/A react: 18.3.0-canary-14898b6a9-20240318 react-dom: 18.3.0-canary-14898b6a9-20240318 typescript: 5.4.5 Next.js Config: output: N/A ``` ### Which area(s) are affected? (Selec…