user service: initial implementation (#17668)

* conceptual user service: initial commit

* reflect review comments

* fix i18n issues and some tests

* implement get user methods

* add license

* reflect review comments

app/server.go

@@ -57,6 +57,7 @@ import (
 	"github.com/mattermost/mattermost-server/v5/services/timezones"
 	"github.com/mattermost/mattermost-server/v5/services/tracing"
 	"github.com/mattermost/mattermost-server/v5/services/upgrader"
+	"github.com/mattermost/mattermost-server/v5/services/users"
 	"github.com/mattermost/mattermost-server/v5/shared/filestore"
 	"github.com/mattermost/mattermost-server/v5/shared/i18n"
 	"github.com/mattermost/mattermost-server/v5/shared/mail"
@@ -158,6 +159,7 @@ type Server struct {
 	limitedClientConfig  atomic.Value
 
 	telemetryService *telemetry.TelemetryService
+	userService      *users.UserService
 
 	serviceMux           sync.RWMutex
 	remoteClusterService remotecluster.RemoteClusterServiceIFace
@@ -407,6 +409,8 @@ func NewServer(options ...Option) (*Server, error) {
 		return nil, errors.Wrap(err, "cannot create store")
 	}
 
+	s.userService = users.New(s.Store.User(), s.Config)
+
 	s.configListenerId = s.AddConfigListener(func(_, _ *model.Config) {
 		s.configOrLicenseListener()