Make UploadableFile::get_data async for AsyncRead

[ColinKinloch]

I've been attempting to bump the version of this in obs-gitlab-runner from 0.5.0to 0.8.0.
It currently stores a map of path strings to tokio::Files for artifacts, but I've changed it to use a Vec<UploadableFile>.

My current implementation does this:

async fn get_data(&self) -> Result<Self::Data<'_>, ()> {
    let file = AsyncFile::open(&self.real_path).await.map_err(|_| {})?;
    Ok(Box::new(file.compat()))
}

I didn't make get_path async as it is used in a non async context and I'm not sure it's necessary.

[andrewshadura]

Nitpick: Preparing (not Prepairing)

[andrewshadura]

You return Result<_,_> but always Ok(_), I assume the reason is that you plan to support returning errors at some point in future?

[andrewshadura]

LGTM except a typo in the commit message.
I’d also expand the commit message to say more why Result is more appropriate.

[ColinKinloch]

Maybe it would be a good idea to utilise async and Result in the demo-runner to make it look less speculative.