Use in custom Node runtimes

## What would you like to have implemented?

Running Node 16 in a Custom Runtime on Lambda, requires this workarond:

```js
process.env.AWS_EXECUTION_ENV = 'AWS_Lambda_nodejs14.x'
const { default: chromium } = await import('chrome-aws-lambda')
```

Given the deprecation of older Lambda runtimes, perhaps the check could just be if AWS_EXECUTION_ENV starts with `AWS_Lambda_`?

