Work off specimen and run_accession like the other pipelines

[muffato]

Description of feature

The samplesheet needs to be updated to support the new "specimen" and "run_accession" columns

[sainsachiko]

@muffato For production run of GAP, these piplines will use readmapping outputs, also, gapops will retrieve read_mapping analysis from readmapping. Thus, no urgency for updating the samplesheet.
To support this, we can allow this 2 columns in the samplesheet but optional (required either sample or specimen,run).
Similar to sanger-tol/variantcalling#145

Note: readmapping is pipeline, read_mapping is analysis