Vendor Update: go-gitlab v0.22.1 -> v0.31.0 (#11136)

* vendor update: go-gitlab to v0.31.0

* migrate client init to v0.31.0

* refactor

vendor/github.com/hashicorp/go-retryablehttp/README.md

@@ -0,0 +1,61 @@
+go-retryablehttp
+================
+
+[![Build Status](http://img.shields.io/travis/hashicorp/go-retryablehttp.svg?style=flat-square)][travis]
+[![Go Documentation](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)][godocs]
+
+[travis]: http://travis-ci.org/hashicorp/go-retryablehttp
+[godocs]: http://godoc.org/github.com/hashicorp/go-retryablehttp
+
+The `retryablehttp` package provides a familiar HTTP client interface with
+automatic retries and exponential backoff. It is a thin wrapper over the
+standard `net/http` client library and exposes nearly the same public API. This
+makes `retryablehttp` very easy to drop into existing programs.
+
+`retryablehttp` performs automatic retries under certain conditions. Mainly, if
+an error is returned by the client (connection errors, etc.), or if a 500-range
+response code is received (except 501), then a retry is invoked after a wait
+period.  Otherwise, the response is returned and left to the caller to
+interpret.
+
+The main difference from `net/http` is that requests which take a request body
+(POST/PUT et. al) can have the body provided in a number of ways (some more or
+less efficient) that allow "rewinding" the request body if the initial request
+fails so that the full request can be attempted again. See the
+[godoc](http://godoc.org/github.com/hashicorp/go-retryablehttp) for more
+details.
+
+Version 0.6.0 and before are compatible with Go prior to 1.12. From 0.6.1 onward, Go 1.12+ is required.
+
+Example Use
+===========
+
+Using this library should look almost identical to what you would do with
+`net/http`. The most simple example of a GET request is shown below:
+
+```go
+resp, err := retryablehttp.Get("/foo")
+if err != nil {
+    panic(err)
+}
+```
+
+The returned response object is an `*http.Response`, the same thing you would
+usually get from `net/http`. Had the request failed one or more times, the above
+call would block and retry with exponential backoff.
+
+## Getting a stdlib `*http.Client` with retries
+
+It's possible to convert a `*retryablehttp.Client` directly to a `*http.Client`.
+This makes use of retryablehttp broadly applicable with minimal effort. Simply
+configure a `*retryablehttp.Client` as you wish, and then call `StandardClient()`:
+
+```go
+retryClient := retryablehttp.NewClient()
+retryClient.RetryMax = 10
+
+standardClient := retryClient.StandardClient() // *http.Client
+```
+
+For more usage and examples see the
+[godoc](http://godoc.org/github.com/hashicorp/go-retryablehttp).