Allow to specify consumergroup in lagtrend slo
requested to merge stu200776/theodolite:feature/356-specify-consumergroup-in-lagtrend-metric into master
When the optional property consumerGroup of the lag trend or lag trend ratio slo is specified, instead of the consumerlag across all consumer groups, only the lag of the specified group is considered. If left blank, no projection is done and the consumer lag is considered across all groups.