Make session setup an extension point for the CLI

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

My ultimate goal is to be able to benchmark the [Vortex](https://github.com/vortex-data/vortex)/DataFusion integration in a consist and reproducible way, especially for ClickBench.

While we have our own tooling, it tends to do through many changes and is not always a perfect match to what DataFusion does, which ends up creating unexpected differences in results.

### Describe the solution you'd like

I would like to be able to use the `datafusion-cli` crate to build our own tool, which should be as close as possible to the existing CLI, just with the ability to modify the session. I think it will be useful for us to include our `FileFormat` stuff, but I can imagine it being useful to test any other extension point in DataFusion that isn't part of the main repo.

### Describe alternatives you've considered

For the time being, I've just created https://github.com/vortex-data/vortex-datafusion-cli which should also help with our versioning, but could be more focused if there's positive response to this idea.

Start with the datafusion-cli crate and compare its existing CLI setup with the vortex-datafusion-cli tool linked in the issue. Define what session customization should be exposed while keeping behavior close to the existing CLI; done means an external tool can modify the session, including adding FileFormat support, without maintaining a separate CLI implementation.

Written by the indexing model from the issue text.