[BulkRNASeq] Workflow fails to launch using approach 3 when gldsAccession is not supplied

[J-81]

Expected behavior

Workflow launch using approach 3 (custom runsheet) should not require setting gldsAccession

Actual behaviour

Workflow checks if gldsAccession is unset and raises an error on attempting to start.

Workaround

Supplying gldsAccession as follows:

nextflow run ... --gldsAccession CustomAnalysis

Note: This will output all results to a directory called CustomAnalysis. The name may be changed if an alternative name for the output directory is desired.