A way to specify the root element for the dynamic source

### Clear and concise description of the problem

Often I need a wrapper component for a `Variant` - sometimes that's to set up mock stores, sometimes it's because the child component is absolutely positioned (or has negative margin/padding) and so the parent needs to offset the child appropriately.

However, adding a wrapper component makes the wrapper component show up in the dynamic source

### Suggested solution

An attribute that can be placed on any element, to make it the root of the dynamic source.

### Alternative

_No response_

### Additional context

_No response_

### Validations

- [X] Follow our [Code of Conduct](https://github.com/histoire-dev/histoire/blob/main/CODE_OF_CONDUCT.md)
- [X] Read the [Contributing Guidelines](https://github.com/histoire-dev/histoire/blob/main/CONTRIBUTING.md).
- [X] Read the [docs](https://histoire.dev/guide/).
- [X] Check that there isn't [already an issue](https://github.com/histoire-dev/histoire/issues) that requests the same feature to avoid creating a duplicate.