Missing features in `Advanced Usage`

[npatki]

• SDV version: 0.13.0

Pointed out by @xamm via Slack: The User Guide for GaussianCopula includes a section for selecting which transformers to use. This section is missing for the other models (CTGAN, CopulaGAN and TVAE).

This led to some confusion about whether the field_transformers is even relevant for the other models. (It is relevant, and is available in the API docs for all models.)

In general, the Advanced Usage section is supposed to be different for tabular models (for eg. GANs have specific hyperparameters). But what about the usage that is common?

To consider:

1. Adding this section to all tabular models docs
2. Creating a section for features that are are common to all models -- similar to constraints