UiTargetCamera() in the bsn! macro is not supported

## Bevy version and features:

Bevy 0.19

## The issue:

Using `UiTargetCamera()` in the bsn! macro is currently not supported.

## Error produced:

```
the trait bound `bevy::prelude::UiTargetCamera: std::default::Default` is not satisfied
```

## Current workarounds:

- For scenes, saving the scene as an entity and inserting `UiTargetCamera(...)` using `insert()`.
- For templates, using `template_value(UiTargetCamera(...))`

Start by reproducing the reported error with UiTargetCamera() in the bsn! macro and trace how that macro handles this component. Compare the existing scene insert() and template_value(UiTargetCamera(...)) workarounds; done means bsn! accepts the component without either workaround and the relevant behavior is covered by a regression test.

Written by the indexing model from the issue text.