Add new storage migration for ertbbox params in Fields

Currently there are ert box params:
```python
xlength: float | None = None
ylength: float | None = None
xinc: float | None = None
yinc: float | None = None
rotation_angle: float | None = None
origin: tuple[float, float] | None = None
```

which when migrated from the older version of storage, these will get assigned `None`. This might end up in a wrong storage state. Therefore we should do an extra storage migration which we populate those values correctly if possible ofc.

Locate the Fields storage-migration entry point and compare the older storage representation with the six ert box parameters listed in the issue. Determine which values can be recovered, then verify that migrating older storage populates recoverable values instead of leaving them as None.

Written by the indexing model from the issue text.