Expose several private functions to allow easier implemenation of `HttpService` and `HttpConnector`

[robalar]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Hi there 👋 I've been trying to implement the HttpService and HttpConnector traits to allow me to trace the HTTP calls that object store is making. However, several functions used in the implementation for HttpService on reqwest::Client (which I am essentially replicating, with the addition of the tracing) are private so I cannot reuse them in my implementation.

These are:

• HttpError::reqwest
• HttpRequestBody::into_reqwest
• ‎ClientOptions::client

Describe the solution you'd like
These functions to be made pub.

Describe alternatives you've considered
None, however, keen to hear if the there would be a better way to trace the calls.

Additional context
N/A

Happy to handle the PR for this (should be trivial), just wanted to make sure it was not misguided!

[tustvold]

Have you considered wrapping the existing HttpConnector instead of duplicating it's functionality?

[robalar]

@tustvold, yeah, the problem being that we already have exisiting implementations for our tracing that wrap reqwests RequestBuilder, so this is the type I want access to. If I were just to wrap the existing HttpConnector, I'd just have access to object stores HttpRequest - which I would need to add the same tracing to (which I think would be do-able, just need to be able to set headers and see errors etc).

However, having access to this methods would be the easiest and reduce maintanence burden for us, but you are obviously increasing your public surface area so its an increased burden for you.

Let me know what you think!

[tustvold]

Realistically we are unlikely to migrate away from reqwest, and so this is probably fine.

Might be worth renaming ClientOptions::client to ClientOptions::connect or something though if we plan to expose it.