Verify that unit statements in inputs are correct

[mabijkerk]

Background
For each input we can specify a unit. For example, in costs_imported_lohc:

- query = UPDATE(CARRIER(lohc, imported_lohc), cost_per_mj, USER_INPUT() / MJ_PER_MWH )
- priority = 0
- max_value = 200.0
- min_value = 0.0
- start_value_gql = present:PRODUCT(V(CARRIER(imported_lohc), "cost_per_mj"),MJ_PER_MWH)
- step_value = 0.1
- unit = euro
- update_period = future

Issue
This unit is not exactly the unit that this input has. In reality, it is not euro, but euro per MWh. In the frontend of ETModel, this is not an issue, because we display the unit correctly there:

- key: costs_imported_lohc
  step_value: 1.0
  unit: "€/MWh"
  command_type: value
  position: 1
  slide_key: costs_hydrogen_import

When you work with the API however, you only see the unit presented in ETSource. This can be confusing, as you can't tell by the unit alone if it's in euro/MJ, euro/kg etc.

Solution
We should go over the unit statements for the inputs in ETSource and make sure that they exactly represent the actual input statement. This is not an urgent issue, we should pick it up at some point @kaskranenburgQ @kndehaan.