Add two agricultural units: decitonne per hectare, kilogram per hecto…

[oldGreyEagle]

OCSM mints ocsm:KiloGM-PER-PLANT because QUDT has no per-plant unit. Two
further units in the same position come up in German arable reporting, and
we would like to reference them from OCSM rather than mint them privately.

DeciTONNE-PER-HA — decitonne per hectare (dt/ha) is the standard
yield unit in German-speaking arable farming; harvest records, advisory
reports and farm software all report in it. QUDT defines
DeciTONNE and
KiloGM-PER-HA but no compound
of the two, so there is currently no registered IRI for it.

KiloGM-PER-HectoL — kilogram per hectolitre is the standard expression
of hectolitre weight (Hektolitergewicht), a routine cereal quality
measurement recorded alongside moisture and protein. QUDT has neither the
compound nor, as far as we found, an equivalent.

Both follow QUDT's compound naming convention, as KiloGM-PER-PLANT does,
so they read consistently beside the units they are built from. The
declarations mirror that existing individual exactly — a qudt:Unit with
label, comment and rdfs:isDefinedBy.

Context: we are mapping German harvest documentation into OCSM and hit both
units immediately. Our implementation currently emits these IRIs in
anticipation of this proposal.