[BI-2234] - Improve exp dataset export file

[HMS17]

Description

Story: BI-2234 - Improve exp dataset export file

Changes to make sub entity dataset export file contain desired columns while not altering the top level export file

• Added backend logic to distinguish between top level and sub entity datasets when exporting and change columns present accordingly
• Updated backend to fill additional sub-entity columns with correct data
• Updated sorting of export file in sub-entity case to also sort by Sub Unit ID (sorting of sub entity dataset UI will be in BI-2755)

Dependencies

n/a

Testing

• Create an experiment with both a top level and sub entity dataset
• Download top level dataset: check that file is sorted env > exp unit id, data is correct, and there are no sub-entity columns
• Download sub entity dataset: check that file is sorted env > exp unit id > sub unit id, data is correct, and there are the following columns present
  -- Exp Unit
  -- Sub-Obs Unit
  -- Exp Unit ID
  -- Sub Unit ID
  -- (Exp Unit Level) ObsUnitID
  -- (Sub-Obs Unit Level) ObsUnitID

Checklist:

• I have performed a self-review of my own code
• I have tested my code and ensured it meets the acceptance criteria of the story
• I have tested that my code works with both the brapi-java-server and BreedBase
• I have create/modified unit tests to cover this change
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to documentation
• I have run TAF: <please include a link to TAF run>