Allow configuring the connection timeout for HTTP clients.

[tobz]

Context

When building an HTTP client, we should be able to configure a timeout specifically for connecting to the downstream target system. This is a simple assurance against extended delays trying to connect to unresponsive systems.

We should be able to trivially support this by dropping down directly to HttpConnector (from hyper-util) when building our HttpsConnector, as it supports setting the connection timeout via HttpConnector::set_connect_timeout.

Notes

One caveat is that set_connect_timeout carries the following note:

If a domain resolves to multiple IP addresses, the timeout will be evenly divided across them.

We should check what Go does, in particular how the Datadog Agent is using net/http/Client, since we know that hosts will commonly resolve to multiple IP addresses when load balanced.. but it's not clear to me if Go/Datadog Agent are also going to try all of those IPs, and enforcing the connect timeout per IP, or just picking one IP, or doing what hyper-util also does, etc....