Add options to configure timeouts

As follow up for #4209, as we get user feedback we should add options to configure timeouts. `reqwest::ClientBuilder` separate total, connection, and read timeouts for HTTP1. I don't think we want to be that granular, but let's wait till we hear feedback. For example, what if total is > that connection + read timeouts? Less? Do people want more granularity or is total timeout (like .NET's `HttpClient`). I'd rather not make a decision so close to GA without having feedback.

When we do, this would be an option on `azure_core::http::ClientOptions` - either a single field or maybe a couple in a nested struct.

Read issue #4209 and the azure_core::http::ClientOptions entry point, then review the reqwest::ClientBuilder timeout model mentioned here. The first task is to gather user feedback and settle whether the API exposes one timeout or several; done means that scope and behavior are agreed before implementation.

Written by the indexing model from the issue text.