Passing in ensemble to parameter config

This is more of a question than an issue: I don`t think we should pass in a complex object like an `ensemble` to the parameter configs, espesially as we are not passing it in to the alternate function here (read_from_runpath), which returns a Dataset.

https://github.com/equinor/ert/blob/dada63a435d34824cf53afd559e0788b663e9629/src/ert/config/parameter_config.py#L58C10-L58C10

For me it would be natual to be able to do:

```python
ds = parameter_config.read_from_runpath(Path("my_file_here"), 0)
parameter_config.write_to_runpath(Path("my_file_here"), 0, ds)
```
without having to go through an `EnsembleAccessor`

Start in src/ert/config/parameter_config.py at the linked line and compare the parameter_config read_from_runpath and write_to_runpath interfaces with the alternate read_from_runpath function. Determine whether a Dataset can be used directly for the read/write flow without an EnsembleAccessor, then confirm the intended API and its tests before considering the issue done.

Written by the indexing model from the issue text.