provider: Enable request/response logging

[radeksimko]

This makes debugging for developers & users of this provider easier by exposing all requests & responses in the log (when >DEBUG severity is set).

Example:

---[ REQUEST ]---------------------------------------
GET /api/v4/user HTTP/1.1
Host: 127.0.0.1:8080
User-Agent: go-gitlab
Accept: application/json
Private-Token: ACCTEST
Accept-Encoding: gzip


-----------------------------------------------------
2019/02/23 00:47:49 [DEBUG] GitLab API Response Details:
---[ RESPONSE ]--------------------------------------
HTTP/1.1 200 OK
Content-Length: 714
Cache-Control: max-age=0, private, must-revalidate
Connection: keep-alive
Content-Type: application/json
Date: Sat, 23 Feb 2019 00:47:49 GMT
Etag: W/"2fb3928e98d70dbe9e8fe1b09573eab8"
Server: nginx
Strict-Transport-Security: max-age=31536000
Vary: Origin
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-Request-Id: bTiJWuX5Se5
X-Runtime: 0.137501

{"id":1,"name":"Administrator","username":"root","state":"active","avatar_url":"https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80\u0026d=identicon","web_url":"http://04e2294d82f2/root","created_at":"2019-02-23T00:46:48.473Z","bio":null,"location":null,"public_email":"","skype":"","linkedin":"","twitter":"","website_url":"","organization":null,"last_sign_in_at":null,"confirmed_at":"2019-02-23T00:46:48.381Z","last_activity_on":null,"email":"admin@example.com","theme_id":1,"color_scheme_id":1,"projects_limit":100000,"current_sign_in_at":null,"identities":[],"can_create_group":true,"can_create_project":true,"two_factor_enabled":false,"external":false,"private_profile":null,"is_admin":true}
-----------------------------------------------------

[roidelapluie]

I will merge this. However can we do something to redact security headers?

[radeksimko]

@roidelapluie The debug log is only available to those who are capable of enabling the debug mode, which are in all (?) cases the same people who provide these (sensitive) credentials through configs or ENV variables in the first place.

We had some early discussions about scrubbing sensitive data internally and we might introduce a solution for that at some point in the future.

[roidelapluie]

Thanks!