Add Tectonic Unit paleoContexts relationship to the datamodel

[melton-jason]

Fixes #6042

This PR does not address the true underlying cause: that it's easy to miss such a relationship in the datamodel to begin with!
A more ideal solution to make sure this problem doesn't happen again is to write a backend test to verify the integrity of the datamodel.
Alternatively, we can remove the separate datamodel file entirely, and only use the Django models and fields, adding any necessary attributes to the fields as need (and implementing a way to enforce integrity for those attributes).

While investigating the Issue, I also uncovered another bug which may be relavent for testing: #6058

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)
• Add automated tests
• Add relevant issue to release milestone
• Add relevant documentation (Tester - Dev)

Testing instructions

• In a database which has a paleo/geo discipline (such as ciscocollections from Adding Paleo Context to COG's child CO causes FieldDoesNotExistError #6042 (comment)), switch to a Collection in a Geo/Paleo discipline
• If not present already, add TectonicUnit to the PaleoContext form (either as Subview or Query Combo Box)
• Navigate to the Data Entry form for a table which has a relationship to PaleoContext (paleo_context_schema and TectonicUnit)
• Add a new or edit an existing PaleoContext which has a related TectonicUnit
  • No error should occur
• On the Tectonic Unit form, display the paleoContexts relationship as a Subview and ensure that PaleoContexts can be added, removed, and edited

[emenslin]

Cannot render tectonic unit as a subview in paleo context

[emenslin]

• Add a new or edit an existing PaleoContext which has a related TectonicUnit
  • No error should occur
• On the Tectonic Unit form, display the paleoContexts relationship as a Subview and ensure that PaleoContexts can be added, removed, and edited

Working now, not sure what happened before but tectonic unit can be rendered as a subview and search has been removed from dependent querycbx

[Areyes42]

• Add a new or edit an existing PaleoContext which has a related TectonicUnit
  • No error should occur
• On the Tectonic Unit form, display the paleoContexts relationship as a Subview and ensure that PaleoContexts can be added, removed, and edited

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Looks good!