typescript-graphql-request ignoring importOperationTypesFrom config option

**Describe the bug**

The `typescript-graphql-request` plugin is ignoring `importOperationTypesFrom` config option.

**To Reproduce**

`codegen.yml`:

```yaml
schema: "http://example.com"
documents: "**/*.gql"
generates:
schema.ts:
plugins:
- typescript
- typescript-operations
config:
onlyOperationTypes: true

sdk.ts:
plugins:
- add:
content: "import * as Types from './schema';"
- typescript-graphql-request
config:
importOperationTypesFrom: Types
```

**Expected behavior**

I expect it to prefix operation types with `Types.` but it doesn't.