Incorporate old Patterns website into training

[bentsherman]

Nextflow Patterns: https://nextflow-io.github.io/patterns/

This website documents various implementation patterns, mostly around channel operators. It's not very visible and it's out of date. I recommend taking the examples that are still useful and incorporating them into the training, e.g. as a "Dataflow Patterns" side quest.

Feel free to rewrite or throw out anything that doesn't fit. This content is very old

See also: https://docs.seqera.io/nextflow/tutorials/static-types-operators

I went through them a year or two ago and wrote down these recommendations:

• Channel duplication: Not needed since DSL2 -- remove

• Sort file pairs by sample name: Use collect and then map with toSorted() to collect and sort a channel of samples

• Create key to combine channels: looks fine, although better to use a samplesheet

• Scatter executions: Use channel.fromList() or fromPath to scatter a collection of inputs. Use flatMap to scatter further if needed. Avoid fromFilePairs, use a samplesheet instead

• Gather results: Use collect to gather a channel into a collection. Use groupBy (>=26.04) or groupTuple to gather a scattered channel into groups (opposite of flatMap)

• Organize outputs: Use the output block

• Other: not sure these are worth keeping

• Advanced patterns: not sure these are worth keeping