Provide ES Modules distribution to allow treeshaking

Importing the single function `composeAndValidate` bloats up my webpack bundle to more than 450KB 🙉 .
```js
import { composeAndValidate } from '@apollo/federation'
```
Example:

- https://github.com/graphql/graphql-js/blob/main/.babelrc-npm.json
- https://github.com/graphql/graphql-js/blob/main/resources/build-npm.js

Start by comparing the package distribution approach in graphql-js's .babelrc-npm.json and resources/build-npm.js, as linked in the issue. Determine how the federation package is currently built and what ES Modules output would be needed for webpack tree shaking. Done means composeAndValidate can be imported without bundling the unused package code.

Written by the indexing model from the issue text.