Add support for NuGet API keys (#20721)

* Add support for NuGet API key.

* lint

* Apply suggestions from code review

Co-authored-by: delvh <dev.lh@web.de>

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

routers/api/packages/api.go

@@ -46,6 +46,7 @@ func Routes() *web.Route {
 	authMethods := []auth.Method{
 		&auth.OAuth2{},
 		&auth.Basic{},
+		&nuget.Auth{},
 		&conan.Auth{},
 	}
 	if setting.Service.EnableReverseProxyAuth {