Improve API and CSV template upload documentation with field values and formats

[scottveirs]

The current Acartia API documentation (at least in or near the CONTRIBUTING.md file) could be enriched by offering allowed values for each field, along with the expected format of the value. It may also be helpful to surface the variable_name used internally for each field.

A good example of this sort of API documentation can be found in the iNaturalist API reference pages:

Ideally, this issue should be tackled after a revision of the data schema (to accommodate acoustic detections and group tags, e.g. for defining tracks of pods, matrilines, or individuals).

A subsequent step could be error checking incoming data to ensure the field names, values, and formats are acceptable -- and providing useful feedback regarding failed quality control checks.