Feat(metadata): Write units attribute in derived datasets (metadata)

[danesss]

Issue

ECDC-3368

Description of work

We modify Value class to also receive a function to write attributes and assume that Value represents a dataset to be written with or without attributes. Previously, Value could be called separately with a group/dataset and a function to respectively create a dataset in the group / attribute in the dataset. I do not see the usefulness of such generalisation, Value class is used exclusively to create derived datasets, so it seems simpler to model it as a dataset and nothing else.

Checklist

• [x] Changes have been documented in changes.md

[cow-bot]

Code Coverage (Lines Exec Cover) TOTAL 5626 3787 67% For more detail see Cobertura report in Jenkins interface

[cow-bot]

Code Coverage (Lines Exec Cover) TOTAL 5626 3785 67% For more detail see Cobertura report in Jenkins interface

[cow-bot]

Code Coverage (Lines Exec Cover) TOTAL 5626 3786 67% For more detail see Cobertura report in Jenkins interface

[cow-bot]

Code Coverage (Lines Exec Cover) TOTAL 5626 3786 67% For more detail see Cobertura report in Jenkins interface

[cow-bot]

Code Coverage (Lines Exec Cover) TOTAL 5626 3786 67% For more detail see Cobertura report in Jenkins interface