Autogen models: type hint Choice fields with Literal[...]

For the autogenerated dataverse table models (#14), "Choice" fields have a few different options their value can take, these are written into the table definition in powerplatform.

It would be nice to automatically find these values somehow and construct a type hint like below for the formatted field (and maybe another with ints for the backend values):

```python
Literal[
"adlib: baseline weight establishment",
"active water restriction",
"adlib: paused water restriction",
"adlib: water restriction complete",
]
```

Maybe if it's not findable with the metadata endpoints, we could add something to the autogen process that allows overriding certain fields so we could just go write down the choices and have it end up in the models.