Fix output units for index function count_occurrences
It seems that the index function
count_occurrences expect output to have units
day. This is however the
proposed_unit, which not consistent with current the current canonical unit
1 as defined by the
standard names. This has probably remained under the radar because I was until recently using a really old version of
index_definition.yml. If simple to fix then target bugfix milestone 13.2, else postpone it to a later milestone.