Standardise measurement values

[ESapenaVentura]

For which schema is a change/update being suggested?

Based on the comment in this PR, I would like to propose standardising the way we represent measured values.

This still requires a discussion to ensure what would be the best way (e.g. adding a standard module could likely create problems if the measurement type does not adapt to the field)

What should the change/update be?

TBD

What new field(s) need to be changed/added?

TBD

Why is the change requested?

Data wranglers will have an easier time when requesting new fields that require a measure term and unit. Having a standardised solution for this will also make it easier for consumers of the metadata to develop solutions to represent this metadata.