Add options to capture HTTP request and response from HttpClient

[mattjohnsonpint]

See getsentry/team-mobile#41

[mattjohnsonpint]

Placeholder until design complete with getsentry/team-mobile#41.

[mattjohnsonpint]

Note, we do already capture URL, Method, and Response Code, as a breadcrumb.

sentry-dotnet/src/Sentry/SentryHttpMessageHandler.cs

Lines 85 to 91 in 910009b

	var breadcrumbData = new Dictionary<string, string>
	{
	{ "url", url },
	{ "method", requestMethod },
	{ "status_code", ((int)response.StatusCode).ToString() }
	};
	_hub.AddBreadcrumb(string.Empty, "http", "http", breadcrumbData);

[mattjohnsonpint]

And we now capture events for HTTP failure responses with #2320