KPI group by Parameter properties

I wish to add a KPI Execution to count the "Number of accessions last updated by year" (and then by institute, by crop).

The current implementation requires me to define a Dimension that will provide the Set<Long> of the years that can then be passed to ExecutionDimension.

1. That requires us to either maintain a NumericListDimension and add all year options manually.
2. Generates a number of observations for years we know no updates have happened.

Idea

Allow for GROUP BY clauses in Execution definition:

• Add group by lastModifiedDate modifier YEAR alias lastModifiedYear
  Generates: select ..., year(_base.lastModifiedDate) lastModifiedYear ... group by lastModifiedYear where ...
• Add group by lastModifiedDate modifier MONTH alias lastModifiedMonth
  Generates: select ..., year(_base.lastModifiedDate) lastModifiedYear, month(_base.lastModifiedDate) lastModifiedMonth ... group by lastModifiedYear, lastModifiedDate where ...

The resulting Observation will therefore go from being a single row with the value (and stddev for AVERAGE) to multiple rows for existing combinations of lastModifiedYear and lastModifiedDate.

The method private Observation getSingleObservation(Query query, Object... params) {} should therefore return List<Observation> and the Observation needs to store the group-by's somewhere.

Could use the "DimensionKey"?