Support for historical / longitudinal indicators

In the Ed-Fi standards and technology have a few places where metric values can be stored, such as EducationOrganizationIndicator or StudentIndicator.

The current Ed-Fi design assumed that these would store only current values.

In the API therefore, the key for these entities is the IndicatorName, which means that multiple indicators of the same name cannot be stored. This means that historical values cannot be stored alongside current values.

Field work has revealed the need to store historical values.

Note that it is unclear if the field work has shown the need to source historical values via API (there are several queries in Tracker on this point)

Tracker tickets: DATASTD-1554, DATASTD-1561, DATASTD-1464