feat(registry): gitlab support (#3107)

* feat(api): gitlab registry type

* feat(registries): early support for gitlab registries

* feat(app): registry service selector

* feat(registry): gitlab support : list repositories and tags - remove features missing

* feat(registry): gitlab registry remove features

* feat(registry): gitlab switch to registry V2 API for repositories and tags

* feat(api): use development extension binary

* fix(registry): avoid 401 on gitlab retrieve to disconnect the user

* feat(registry): gitlab browse projects without extension

* style(app): code cleaning

* refactor(app): PR review changes + refactor on types

* fix(gitlab): remove gitlab info from registrymanagementconfig and force gitlab type

* style(api): go fmt

* feat(api): update APIVersion and ExtensionDefinitionsURL

* fix(api): fix invalid RM extension URL

* feat(registry): PAT scope help

* feat(registry): defaults on registry creation

* style(registry-creation): update layout and text for Gitlab registry

* feat(registry-creation): update gitlab notice

api/http/proxy/gitlab.go

@@ -0,0 +1,38 @@
+package proxy
+
+import (
+	"errors"
+	"net/http"
+	"net/url"
+)
+
+type gitlabTransport struct {
+	httpTransport *http.Transport
+}
+
+func newGitlabProxy(uri string) (http.Handler, error) {
+	url, err := url.Parse(uri)
+	if err != nil {
+		return nil, err
+	}
+
+	proxy := newSingleHostReverseProxyWithHostHeader(url)
+	proxy.Transport = &gitlabTransport{
+		httpTransport: &http.Transport{},
+	}
+
+	return proxy, nil
+}
+
+func (transport *gitlabTransport) RoundTrip(request *http.Request) (*http.Response, error) {
+	token := request.Header.Get("Private-Token")
+	if token == "" {
+		return nil, errors.New("No gitlab token provided")
+	}
+	r, err := http.NewRequest(request.Method, request.URL.String(), nil)
+	if err != nil {
+		return nil, err
+	}
+	r.Header.Set("Private-Token", token)
+	return transport.httpTransport.RoundTrip(r)
+}