Update GatherSampleEvidence & TrainGCNV docs

[VJalili]

This PR extends the documentation of the GatherSampleEvidence and TrainGCNV workflows. Specifically, it implements the following changes.

• Extends the documentation on the inputs and outputs of the GatherSampleEvidence, GatherBatchEvidence, and TrainGCNV workflows.
• Instead of enlisting inputs and outputs, they are formatted as sections. This enables referencing them individually, which is useful when referencing an output of workflow passed as input to another workflow. The header level is set to 4 (i.e., ####); hence, these sections are not rendered in the quick navigation section (top-right panel) to reduce clutter.
• Adds diagrams for better visualization of up and downstream dependencies of workflows, currently implemented for GatherSampleEvidence, GatherBatchEvidence, EvidenceQC, and TrainGCNV workflows.
• Add JS & CSS components to enable highlighting text, which is used in this PR to tag optional outputs.