Add changes for tracking scib-metrics in autotune

[martinkim0]

Here's an example code snippet for how this works with SCVI:

import scvi
from scvi.autotune import ModelTuner
from scvi.train._scib_callback import ScibCallback

adata = scvi.data.synthetic_iid()
model_cls = scvi.model.SCVI
model_cls.setup_anndata(adata, batch_key="batch", labels_key="labels")

tuner = ModelTuner(model_cls)
tuner.fit(
    adata,
    use_defaults=True,
    metric="validation Batch correction",  # necessary
    train_kwargs={"callbacks": [ScibCallback(stage="validation")]},  # necessary
    validate_metrics=False,  # necessary
)

Code is not nice yet as the TrainingPlan has to accumulate and store the raw counts, latent representation, batches, and labels for this to work.