Modular embedding wizard: Let users pick the data picker entity types

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**What problem will this feature request solve?**
Currently, when using the modular embedding wizard we apply the following logic: "if models > 2, then set the snippet to entity-types=\["model"\]

But folks might want to customize that, either to use models even w/ 1 or 2 models only, or to enable folks to query tables even if there are more than 2 models.

**Describe the solution you'd like.**
Let users choose the entity models to show in data picker.

**How does this feature request impact you?**
Discussed this internally based on feedback from PAs. [Slack]()

**Additional information**

Start by locating the modular embedding wizard and the current logic that sets entity-types=["model"] when there are more than two models. Trace how the data picker options and generated snippet are assembled. Done means users can choose the entity types shown, including models with one or two models and tables when more than two models exist.

Written by the indexing model from the issue text.