Allow specifying energy at top level of LoadCentreCollect

For keys inside `WithSample` I can do:
```
LoadCentreCollect.model_validate({
"sample_id": 123
...
"robot_load_then_centre": {}
"multi_rotation_scan": {}
})
```
and the information will propagate through to `robot_load_then_centre` and `multi_rotation_scan` but for `demand_energy_ev` I have to specify this on both the `robot_load_then_centre` and `multi_rotation_scan` and I can't at the top level. I should be able to specify at the top level and it be filled in for both "child" params.

## Acceptance Criteria
- I can specify energy at the top level of `LoadCentreCollect`
- When I do I do not need to specify it to the underlying params