Reload languageServer on `localSchemaFile` change.

For now, I'm using monorepo with server and client. And when my watch scripts regenerate schema file I need to manually reload `Apollo: Reload Schema` (`apollographql/reloadService`).

It will be nice if vs-code plugin reloads automatically with new `localSchemaFile` data.

Need to extend somehow the following code:
https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo-language-server/src/server.ts#L133

### But for now I found a workaround
You need to install [File Watcher](https://marketplace.visualstudio.com/items?itemName=AppulateInc.filewatcher) extension and add the following config to : `.vscode/settings.json`:
```js
{
"filewatcher.commands": [
{
"match": "\\.graphql*",
"isAsync": true,
"cmd": "touch ${workspaceRoot}/apps/client/apollo.config.js",
"event": "onFileChange"
}
]
}
```

`touch` command will refresh `apollo.config.js` and Apollo for VSCode will catch these changes and reload the schema file.

Start with packages/apollo-language-server/src/server.ts around line 133 and trace how changes to apollo.config.js reach the VS Code plugin's reloadService. Reproduce the monorepo case by regenerating the localSchemaFile, then verify that the language server reloads automatically without the File Watcher workaround or manual Apollo: Reload Schema command.

Written by the indexing model from the issue text.