Change `determination_deails` to `determination`

[mihow]

determination used to be a direct reference to a Taxon object. Now it is a more complex object with more context (user, date, taxon, etc). We added a new determination_details property with this context in the Occurrence API endpoints. However we should create a new Determination object with the important context as properties rather than being an alias for just Taxon. Update this in ami.main.models and ami.main.serializers. Some related comments are in models.py here: https://github.com/RolnickLab/ami-platform/blob/ddeae3dd8dc02908640d6be7bb776c39f08122c9/ami/main/models.py#L1238-L1240