Implementation endpoint for APIv4: GET /teams/name/{name} (#5473)

* APIv4: GET /teams/name/{name}

Signed-off-by: Saturnino Abril <saturnino.abril@gmail.com>

* reorganized test with SystemAdminClient

Signed-off-by: Saturnino Abril <saturnino.abril@gmail.com>

app/team.go

@@ -304,6 +304,7 @@ func GetTeam(teamId string) (*model.Team, *model.AppError) {
 
 func GetTeamByName(name string) (*model.Team, *model.AppError) {
 	if result := <-Srv.Store.Team().GetByName(name); result.Err != nil {
+		result.Err.StatusCode = http.StatusNotFound
 		return nil, result.Err
 	} else {
 		return result.Data.(*model.Team), nil