Why

This PR addresses the following problem / context:

• A user needs to record the reason for a NULL water level value using a controlled vocabulary
• FieldEventContactAssociation is an unclear name
• The geothermal group needs to be consulted before their data are imported and legacy code is cluttering the code base

How

Implementation summary - the following was changed / added / removed:

• Changed level_status to value_reason and made it a non-nullable field for all observations. The value_reason field allows users to provide context for a single observation value. This is particularly important for NULL water levels so we can deduce which are NULL because the well is dry (as opposed to other reasons like an obstruction)
• FieldEventContactAssociation was renamed FieldEventParticipant for clarity
• legacy geothermal code in the observation table was removed to declutter the code base

Notes

Any special considerations, workarounds, or follow-up work to note?

• The consensus on when a groundwater level observation is NULL:
  • If anything occurs before an attempt is made to retrieve a groundwater level and it prevents such an action, then a FieldEvent record is made but no Observation or Sample records are made. It is then noted in the FieldEvent record why this happened. A restricted vocabulary could be useful, but there are so many things that can go wrong we thought to just have it noted in the notes field. This could be anything from a flat tire to a locked gate to muddy roads to a destroyed well.
    • If a well is found to be destroyed there should be a workflow to update the StatusHistory, too.
    • A WaterLevels record that indicates a destroyed well will create a FieldEvent record but no sample or observation
  • If anything happens after a sample/observation has been attempted (such as an obstruction, equipment failure, or dry well), then an observation record is made, value is set to NULL, and controlled vocabulary is used in value_reason to indicate why it is NULL. As written above, this is particularly important for water levels so we can deduce if a well is dry or not.