log: display client error messages when possible as warnings

[Fishrock123]

This should help demystify some cases when client errors are determined by parsing and propagated via ?.

Description

Makes the logger display an associated error message when this warning occurs, if possible.

Also clarified that a client error occured.

Motivation and Context

For never users some cases of client errors being caused by e.g. body parsing and then propgated via ? may be unobvious. This helps demystify that.

How Has This Been Tested?

Manual curl to the json example. Output:

tide::log::middleware Client error --> Response sent
    message missing field `name` at line 1 column 2
    method POST
    path /submit
    status 422
    duration 73.9µs

Checklist:

• I have read the CONTRIBUTING document.
• All new and existing tests passed.

[jbr]

👍