Work with multiple projects and/or support GraphQL Config

In our project, we're working with multiple different graphs.
Sometimes these graphs are actually external services we do not control but we write queries to target them.
We've been using [VS Code GraphQL: Language Feature Support](https://marketplace.visualstudio.com/items?itemName=GraphQL.vscode-graphql) extension for GraphQL LSP

I've been setting up GraphQL Config https://the-guild.dev/graphql/config to tell the VS Code extension which files should use which schema

Here's the config we are currently using

graphql.config.js

```js
const mxSchema = "backend/packages/graphql-schema/schema.gen.graphql";

module.exports = {
projects: {
default: {
schema: mxSchema,
},
"backend-tests": {
schema: mxSchema,
documents: ["backend/api/src/**/__tests__/**/*.spec.ts"],
},
"server-rendering": {
schema: mxSchema,
documents: [
"backend/server-rendering/src/graphql/**/*!(.gen).{ts,tsx}",
"backend/server-rendering/src/modules/**/graphql/**/*!(.gen).{ts,tsx}",
],
},
"work-order-asset-snapshots": {
schema: mxSchema,
documents: ["backend/graphql/src/mutations/helpers/workOrderAssetSnapshot/**/*.{ts,tsx}"],
},
frontend: {
schema: mxSchema,
documents: [
"frontend/src/**/*.gql!(.gen).{ts,tsx}",
"frontend/src/graphql/**/*!(.gen).{ts,tsx}",
"frontend/src/modules/**/graphql/**/*!(.gen).{ts,tsx}",
"native/src/shared-all/graphql/**/*!(.gen).{ts,tsx}",
"native/src/shared-clients/graphql/**/*!(.gen).{ts,tsx}",
],
},
dashboard: {
schema: mxSchema,
documents: [
"dashboard/src/**/*.gql!(.gen).{ts,tsx}",
"dashboard/src/graphql/**/*!(.gen).{ts,tsx}",
"dashboard/src/modules/**/graphql/**/*!(.gen).{ts,tsx}",
"native/src/shared-all/graphql/**/*!(.gen).{ts,tsx}",
"native/src/shared-clients/graphql/**/*!(.gen).{ts,tsx}",
],
},
native: {
schema: mxSchema,
documents: [
"native/src/**/*.gql!(.gen).{ts,tsx}",
"native/src/graphql/**/*!(.gen).{ts,tsx}",
"native/src/modules/**/graphql/**/*!(.gen).{ts,tsx}",
"native/src/shared-all/graphql/**/*!(.gen).{ts,tsx}",
"native/src/shared-clients/graphql/**/*!(.gen).{ts,tsx}",
],
},
gpl: {
schema: "gql-gen/gpl.gen.graphql",
documents: "backend/common/src/core/gpl/*!(.gen).ts",
},
metal: {
schema: "backend/node_modules/@metal/graphql/schema.gen.graphql",
documents: "backend/common/src/core/metal/*!(.gen).ts",
},
},
};
```

You'll notice that we have multiple "client" applications targeting the same schema which allows to better understand which fragments belongs to which project.
Also at the end you'll notice that have a local copy of the `gpl` project that is an external api we call and the `metal` project has an sdk providing the schema that we're using as well.

Worth noting that we have a separate config for GraphQL Codegen, because the VS Code GraphQL LSP extension doesn't support multiple schema files even though the GraphQL Config standard supports it. So we stitch all our schemas into 1 big schema file and pipe this into the extension instead

Since we are starting to look into Federation, we are investigating better extension to empower our devs and was hoping Apollo's extension would support the GraphQL Config for a more standardized way to provide a great GraphQL experience to our developpers.

Start by reviewing the extension's current schema and document configuration, then compare it with the GraphQL Config projects example in the issue. Done should mean the extension can identify multiple projects, associate documents with their configured schemas, and support external schema files without requiring one stitched schema.

Written by the indexing model from the issue text.