Adds support for GMs in shared channels (#31403)

* Adds support for GMs in shared channels

* Fix linter

* Remove creatorID from slack call

---------

Co-authored-by: Miguel de la Cruz <miguel@ctrlz.es>

server/platform/services/slackimport/slackimport.go

@@ -88,7 +88,7 @@ type Actions struct {
 	AddUserToChannel       func(request.CTX, *model.User, *model.Channel, bool) (*model.ChannelMember, *model.AppError)
 	JoinUserToTeam         func(*model.Team, *model.User, string) (*model.TeamMember, *model.AppError)
 	CreateDirectChannel    func(request.CTX, string, string, ...model.ChannelOption) (*model.Channel, *model.AppError)
-	CreateGroupChannel     func(request.CTX, []string) (*model.Channel, *model.AppError)
+	CreateGroupChannel     func(request.CTX, []string, string, ...model.ChannelOption) (*model.Channel, *model.AppError)
 	CreateChannel          func(*model.Channel, bool) (*model.Channel, *model.AppError)
 	DoUploadFile           func(time.Time, string, string, string, string, []byte) (*model.FileInfo, *model.AppError)
 	GenerateThumbnailImage func(request.CTX, image.Image, string, string)
@@ -764,7 +764,7 @@ func (si *SlackImporter) oldImportChannel(rctx request.CTX, channel *model.Chann
 		if creator == nil {
 			return nil
 		}
-		sc, err := si.actions.CreateGroupChannel(rctx, members)
+		sc, err := si.actions.CreateGroupChannel(rctx, members, "")
 		if err != nil {
 			return nil
 		}