Adding minimal fee option for volume adding (FE)

[MariusJulius]

Related to: https://github.com/keeleinstituut/tv-tolkevarav/issues/684

As there was problem with adding minimal fee then it was temporarily hidden from the volume unit selection.

To-do:

• please add minimal fee (miinimumtasu) option back for adding volume

[plakitkelly]

Can't save minimal fee

{message: "The selected unit type is invalid.",…} errors : {unit_type: ["The selected unit type is invalid."]} message : "The selected unit type is invalid."

[MariusJulius]

@KaarelKa what would be the estimated and when you can fix it?