Set temporal representativeness attribute for processes to inventory vintage, not target year

[dt-woods]

For example, the processes in the 2016 baseline have their temporal attribute set to 2018, which represents the modeling year of interest and is not reflective of the underlying process data.

Let's assume Time is the representation of the underlying inventory. Perhaps add clarity to the time description field.

See time description in olca-schema, including "validFrom" and "validUntil."

[dt-woods]

See https://github.com/KeyLogicLCA/ElectricityLCI/commit/aa4f6cb550e727ec6564f629fd42a44ccd276d8a