Allow for filtering of properties when using `PromptRunner.createObject`

[poutsma]

When using PromptRunner with JPA entities, or any other domain types with database-backed identifier properties, the LLM will hallucinate its own identifier which obviously not correspond with the existing ones in the database.

We should allow users to filter the properties that should be generated, for instance through setting (dis)allowed fields, like Spring's DataBinder.

Another example of this would be auditing fields (in Spring Data), which should also not be generated by an LLM.

One way to solve this would be to set a default value, and later filtering that out.