MarkDuplicates: Instead of adding the read group of a read to the key, picard always adds "RG"

[michaelgatzen]

User brought this to our attention in this forum post along with a suggestion to fix: https://gatk.broadinstitute.org/hc/en-us/community/posts/21784610948635-Picard-MarkDuplicates-doesn-t-consider-the-Read-Group-when-finding-paired-reads?page=1#community_comment_21964307126811