Coverage metrics: use `region` suffix irrespective of pattern

[pdiakumis]

In

dracarys/R/dragen.R

Line 847 in 23841a4

dragen_coverage_metrics_read <- function(x) {

we handle each case of qc/target/genome region separately, but we can simplify the column binding by naming those the same. We can add a 'region' column to distinguish between e.g. tmb/wgs.