## Description
- Add stories for storybook
- Add unit tests. Some case are not covered due to lack of clear
requirements and will be added later
- Fix bug where `username` is `undefined`
Fixes #`Issue Number`
_or_
Fixes `Issue URL`
> [!WARNING]
> _If no issue exists, please create an issue first, and check with the
maintainers if the issue is valid._
## Automation
/ok-to-test tags="@tag.Sanity"
### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results -->
> [!TIP]
> 🟢🟢🟢 All cypress tests have passed! 🎉🎉🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/11177693011>
> Commit: ba99a27d5956a74dade5ae54998056bd2d3d6a44
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=11177693011&attempt=2"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Sanity`
> Spec:
> <hr>Fri, 04 Oct 2024 10:27:03 UTC
<!-- end of auto-generated comment: Cypress test results -->
## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [ ] No
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
## Release Notes
- **New Features**
- Introduced a new Storybook configuration for the `AIChat` component,
showcasing various states including `Main`, `EmptyHistory`, `Loading`,
and `WithHistory`.
- **Improvements**
- Enhanced testability of the `AIChat` and `ChatTitle` components by
adding `data-testid` attributes.
- Updated `AIChat` component to streamline props and improve rendering
logic.
- **Bug Fixes**
- Ensured the `username` prop defaults to an empty string in the
`WDSAIChatWidget` component.
- **Tests**
- Added a comprehensive test suite for the `AIChat` component,
validating its rendering and functionality across different scenarios.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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