Proposal: add --debug flag to `deploy` (print out HTTP request)

During provider development i've found it helpful to log the the entire request/response sent from the CLI to the gateway.

Expected Behaviour

faas cli deploy --debug

Current behaviour

$faas deploy 
Deploying: echo.
Unexpected status: 400, message: Please provide a valid route /function/function_name.

Function 'echo' failed to deploy with status code: 400

Future behaviour with debug flag

$ faas deploy --debug                                    
Deploying: echo.
WARNING! Communication is not secure, please consider using HTTPS. Letsencrypt.org offers free SSL/TLS certificates.
2019/05/10 18:54:21
-------- deploy request:echo --------
PUT /system/functions HTTP/1.1
Host: 127.0.0.1:8080
Authorization: Basic YWRtaW46OGFmYzg4N2YxMjM3NGViZmMwN2I0ZTZjMTQ3MzY5Y2Y1NzQ5MGNmZTA1N2ZkOGIyYTE1ZTk2MWEwZjc2Y2ZhNQ==

{"service":"echo","image":"ewilde/echo:latest","network":"","envProcess":"python index.py","envVars":{},"constraints":null,"secrets":[],"labels":{},"annotations":{},"limits":null,"requests":null,"readOnlyRootFilesystem":false}
-------------------------------------
2019/05/10 18:54:21
-------- deploy response:echo --------
HTTP/1.1 400 Bad Request
Content-Length: 53
Content-Type: text/plain; charset=utf-8
Date: Fri, 10 May 2019 17:54:21 GMT

Please provide a valid route /function/function_name.
-------------------------------------

Unexpected status: 400, message: Please provide a valid route /function/function_name.

I have a private fork with the above functionality, if it's something the community wants I can PR it in / or adapt based on feedback.

Alternatives

• Run faas-cli through a proxy which logs request/response (not such great DX?)

Extensions

• Flag could get proxied as a header X-OpenFaaS-Trace to gateways / provider which could debug log request/response as each hop

Start at the deploy command entry point and the CLI's HTTP request path; the issue names no files or tests. Compare normal output with the proposed --debug transcript. Done means faas-cli deploy --debug prints the deploy request and response while preserving existing behavior without the flag.