In JavaScript, you can define the assistant persona by calling `withPersonaOptions` when creating the `AiChat` component.
The `withPersonaOptions` function takes an object with two properties: `assistant` and `user`. The `assistant` property is
what you use to define the assistant persona, as shown in the example below.

```javascript
const aiChat = createAiChat()
    .withAdapter(adapter)
    .withPersonaOptions({
        assistant: {
            name: 'HarryBotter',
            avatar: 'https://docs.nlkit.com/nlux/images/personas/harry-botter.png',
            tagline: 'Mischievously Making Magic With Mirthful AI!'
        }
    });
```

The object passed to the `assistant` property should match the following interface:

```typescript
interface AssistantPersona {
    name: string;
    avatar: string | HTMLElement;
    tagline?: string;
}
```
