Standardize logging of HTTP interactions in the framework

Expected behavior

It should be possible to easily log the nature of HTTP invocations, including performance metrics, request & response content, and the like. This should be limited in Production contexts to both respect user privacy and conserve log resources.

URLSessionTaskDelegate might provide a centralized location to intercept requests & responses, as well as performance metrics via URLSessionTaskMetrics.

Actual behavior

At the moment, it is possible to inspect this information via manual debugging, but the logging in-place is not uniform. Performance metrics require manual instrumentation, as observed in this PR.

Steps to reproduce the behavior

N/A

WordPressKit Environment

• WordPressKit Version : WordPressKit v4.0.0 & before
• OS : iOS 10.x - 12.x
• Device : all devices
• Xcode Version : Xcode 10.2

Additional Context

N/A