Rename `current_education` to `current_education_enrolment`

[MaxGhenis]

https://github.com/PolicyEngine/openfisca-uk/blob/086b900770888125e4d1b4bc694a05cead4f81a3/openfisca_uk/variables/demographic/person.py#L178

To clarify the distinction from attainment.

[vahid-ahmadi]

@MaxGhenis — this is a coordinated rename: current_education is referenced in 16 files here plus 5 files in policyengine-uk-data (including datasets/frs.py, which populates the column for microsimulation), so a rename in this repo alone would break dataset loading.

Three ways to land it:

1. Coordinated PRs in policyengine-uk + policyengine-uk-data landed together.
2. Staged with a deprecation alias (like the recent labor → labour LSR rename in labor -> labour in LSR parameters #853): rename here, keep current_education readable as an alias, migrate the data repo in a follow-up.
3. Close as not worth the churn if the enum + variable label already clarify the distinction from highest_education.

Which would you like?