graphql executor plugin

Looks like there's no plugin for plain [graphql](https://www.npmjs.com/package/graphql) package. This kind of plugin would come in handy when testing backend resolvers. The plugin would automatically wrap the executable schema (path taken from plugin settings) and be strongly typed so that tests could gain better type safety. An example usage could look like:

`const result = await executeMyGaphqlQuery(ctx, variables);`

The generated code would roughly look something like:

```
export function execute${operationName}(ctx: any, variables: ${operationVariablesTypes}): Promise> {
return graphql(schema, documentVariableName, undefined, ctx, variables);
};
```

```typescript
export function executeMyGaphqlQuery(ctx: any, variables: Variables): Promise> {
return graphql(schema, documentVariableName, undefined, ctx, variables);
};`
```