use Debug impl for generic Reqwest errors to provide more info

[erratic-pattern]

Closes #6377

This should help in the interim to identify specific causes of, sometimes confusing, network related errors. I think this change should be temporary until we can find a better way to improve error messages.

[tustvold]

I think this runs the risk of inadvertently exposing details that shouldn't be rendered in logs, I therefore think we should instead look to improve the logging in a more targeted fashion.

[erratic-pattern]

I think this runs the risk of inadvertently exposing details that shouldn't be rendered in logs, I therefore think we should instead look to improve the logging in a more targeted fashion.

So I think there's two ways to go about this:

1. move away from snafu and do explicit Display impls that show more information about the reqwest error.

2. convert reqwest::Error to a new internal wrapper type which classifies the errors based on category and includes information like cause, and provides its own snafu-based Display implementation so that we can customize how reqwest errors are displayed.

Do you have any preference here? I think the latter is possibly a cleaner option. I'd just like to get some kind of permission before I go mucking around with the existing error conventions in the library.

[tustvold]

I would recommend taking a step back and working out what it is we are wanting to expose beyond what we do currently, and getting consensus on the ticket. As it stands I am a little unsure what we're aiming to achieve here, and therefore struggle to advise on how best to achieve it.

The reqwest maintainer states that users should walk the error chain if they want more detailed error information - seanmonstar/reqwest#2373 (comment). There is therefore a reasonable argument that this custom logic doesn't even belong in this crate, and users wanting more detailed errors should look to display the error chain.