Add example implementing filter pushdown

### Is your feature request related to a problem or challenge?

@pgwhalen says on https://github.com/apache/datafusion-site/pull/161/changes#r2972139725

> As someone who struggled with implementing filter pushdown in a custom table provider before, it would be helpful if there was a section with examples on actually implementing it, just to specifying that the table provider supports it. Going from filters: &[Expr] to something more useful was pretty intimidating for me as a newbie. I ended up learning about LiteralGuarantee::analyze from the pruning_predicate.rs example and that was the big unlock, but as someone not familiar with database internals terminology, it was nonobvious initially.

### Describe the solution you'd like

It would be cool to add an example that shows how to use PruningPredicate and LiteralGuarantee to decide among files based on predicates, for example

### Describe alternatives you've considered

_No response_

### Additional context

_No response_