Change default behavior of GatherSampleEvidence to skip running module metrics

[VJalili]

The GatherSampleEvidence workflow is set to run GatherSampleEvidenceMetrics by default. However, running that task requires setting values for the optional inputs primary_contigs_fai and sv_pipeline_base_docker. Therefore, the GatherSampleEvidence workflow currently fails if only the required input is provided.

Since WDL does not support making the optional inputs as required w.r.t to the value of another argument, and Terra UI lacks features to hint to a user about such a chain of requirements, in-line comments in code seem the only option, as it is implemented. However, in-code comments are less user-friendly and should be reserved for developers and power users only.

Skipping to run this task as a default behavior results in the successful execution of the workflow if only the required input is provided seems to be a better design and improved UX.