LDAP: refactoring (#17479)

* LDAP: use only one struct

* Use only models.ExternalUserInfo

* Add additional helper method :/

* Move all the helpers to one module

* LDAP: refactoring

* Rename some of the public methods and change their behaviour

* Remove outdated methods

* Simplify logic

* More tests
  There is no and never were tests for settings.go, added tests for helper
  methods (cover is now about 100% for them). Added tests for the main
  LDAP logic, but there is some stuff to add. Dial() is not tested and not
  decoupled. It might be a challenge to do it properly

* Restructure tests:
   * they wouldn't depend on external modules
   * more consistent naming
   * logical division

* More guards for erroneous paths

* Login: make login service an explicit dependency

* LDAP: remove no longer needed test helper fns

* LDAP: remove useless import

* LDAP: Use new interface in multildap module

* LDAP: corrections for the groups of multiple users

* In case there is several users their groups weren't detected correctly

* Simplify helpers module

pkg/api/http_server.go

@@ -25,6 +25,7 @@ import (
 	"github.com/grafana/grafana/pkg/registry"
 	"github.com/grafana/grafana/pkg/services/datasources"
 	"github.com/grafana/grafana/pkg/services/hooks"
+	"github.com/grafana/grafana/pkg/services/login"
 	"github.com/grafana/grafana/pkg/services/quota"
 	"github.com/grafana/grafana/pkg/services/rendering"
 	"github.com/grafana/grafana/pkg/setting"
@@ -66,6 +67,7 @@ type HTTPServer struct {
 	QuotaService        *quota.QuotaService      `inject:""`
 	RemoteCacheService  *remotecache.RemoteCache `inject:""`
 	ProvisioningService ProvisioningService      `inject:""`
+	Login               *login.LoginService      `inject:""`
 }
 
 func (hs *HTTPServer) Init() error {