[tutorial] Intermediate MNIST

[romesco]

Pickup where we left off in Basic Tutorial

To address:

• Configuring the model
• Configuring the dataset
• Swapping in and out different Optimizers/Schedulers

Another thing to think about diving further into:
Quoting @omry:

Complexity here has multiple dimensions:
Config style:
* File based
* Dataclass bases
* Dataclass as schema for files
Config modeling:
* Single config
* Config groups