[object_store] Run requests on a different tokio runtime

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
There are cases where one would like to use a different Tokio threadpool for making object store requests. For example, see this ticket in DataFusion

• Document DataFusion Threading / tokio runtimes (how to separate IO and CPU bound work) datafusion#12393

Note it is now possible to use object_store without reqwest (and therefore potentially without tokio), however I think tokio is still important enough to warrant this feature

• Decouple ObjectStore from Reqwest arrow-rs#7183

Describe the solution you'd like
I would like some way, with an example, of making object store requests from an async function running on one tokio runtime (Handle) and execute on another

Describe alternatives you've considered
@tustvold has a proposal to do this in apache/arrow-rs#7253, so this is the corresponding ticket explaining the rationale

Additional context

[tustvold]

and therefore potentially without tokio

This isn't actually true - filed #1.

[ndemir]

Just to be clear, this request will extend the current interface. Right?

Example Usage:

use object_store::{aws::AmazonS3Builder};
use tokio::runtime::Handle;

// Create a dedicated IO runtime 
let io_runtime = tokio::runtime::Builder::new_multi_thread()
    .worker_threads(4)
    .thread_name("object-store-io")
    .build()
    .unwrap();

// Create store with specific runtime handle
// or, something like that
let store = AmazonS3Builder::from_env()
    .with_runtime_handle(io_runtime.handle().clone())
    .build()?;

[alamb]

I am not 100% sure @ndemir -- one of the big things I want to do before merging apache/arrow-rs#7253 is write up some more documentation on how it would be used (and an example as you show is important)

[ndemir]

@alamb

I initially thought this was a new issue, but I realized that PR apache/arrow-rs#7253 already addresses and closes it.

I had asked the previous question to clarify whether this issue was expecting a new change.

Long story short, my comment can be ignored since I mistakenly assumed this was a new issue without an existing PR.

[alamb]

Migrating from arrow-rs issue #7304