Add autofetching for useful pks

[patricklatimer]

New records being added often have foreign keys they need to provide, such as test_pk in the following example:

class SlimsWaterlogResult(SlimsBaseModel):
    """Model for a SLIMS Waterlog Result, the daily water/weight records

    Examples
    --------
    >>> from aind_slims_api.core import SlimsClient
    >>> from aind_slims_api import models
    >>> client = SlimsClient()
    >>> mouse = client.fetch_model(models.SlimsMouseContent, barcode="00000000")
    >>> test_pk = client.fetch_pk("Test", test_name="test_waterlog")

    Write waterlog result.
    >>> waterlog_result = client.add_model(
    ...  models.SlimsWaterlogResult(
    ...   mouse_pk=mouse.pk,
    ...   date=datetime(2021,1,1),
    ...   weight_g=20.0,
    ...   water_earned_ml=5.0,
    ...   water_supplement_delivered_ml=5.0,
    ...   water_supplement_recommended_ml=5.0,
    ...   total_water_ml=10.0,
    ...   comments="comments",
    ...   workstation="aibs-computer-id",
    ...   test_pk=test_pk,
    ...  )
    ... )
"""

It shouldn't be on the user to fetch those, we should add some way that the client lazily fetches those kinds of pks when it needs them, or populates the cache based on already-fetched models of that same type.

[mochic]

I think that the Mouse interface in #33 is a really convenient way to interact with the data. Maybe this autofetching can go there. I believe automatic behavior at the top level is easiest (easier to toggle off too). A custom type for fetching pks could also just be added to models too if you think automatic fetching on the model level is still valuable. In my mind it would be a serialization of the args fed into fetch_pks.

[patricklatimer]

I think you're right that this belongs in the Operations code, I'll close this.