List: Lists fixed width coverage buckets for a read group set, each of which correspond to a range of a reference sequence. Each bucket summarizes coverage information across its corresponding genomic range. For the definitions of read group sets and other genomics resources, see [Fundamentals of Google Genomics](https://cloud.google.com/genomics/fundamentals-of-google-gen omics) Coverage is defined as the number of reads which are aligned to a given base in the reference sequence. Coverage buckets are available at several precomputed bucket widths, enabling retrieval of various coverage 'zoom levels'. The caller must have READ permissions for the target read group set.