[DISCUSSION] Add `DedicatedExecutor` into the DataFusion crates to make using multiple threadpools easier

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

- Related to https://github.com/apache/datafusion/issues/12393

### Describe the solution you'd like

As explained on the following PR:
- https://github.com/apache/datafusion/pull/14286

I implemented a version of `DedicatedExecutor` and an example showing how to use multiple thread pools with DataFusion. However, the example is currently very large as it uses an abstraction called `DedicatedExecutor` to manage sending work back and forth between the runtimes

If users want to do the same thing, they will need to copy `DedicatedExecutor` into their code (or make something similar).

### Describe alternatives you've considered

If `DedicatedExecutor` is a useful API for multiple people I think we should consider moving it into one of the core crates

### Additional context

_No response_

Start by reading the related issue 12393 and pull request 14286, which contain the current DedicatedExecutor implementation and example. Determine whether the abstraction belongs in a DataFusion core crate and what API maintainers want; the work is done when the crate placement and public API are agreed and implemented with appropriate coverage.

Written by the indexing model from the issue text.