create hello-nf-on-vwb example

[samhornstein]

Summary

Adds nextflow/hello-nf-on-vwb/, a minimal, self-contained Nextflow pipeline that runs unchanged locally or on Verily Workbench via Google Batch. Modeled on the official
Hello Nextflow training: reads greetings from a CSV, uppercases them in parallel, collects into one file. The point is the
Workbench wiring (profiles, params, containers, GCS work directory), not the string processing.

Also links the new example from nextflow/README.md.

What's included

• Pipeline — main.nf plus modules/ (sayHello, convertToUpper, collectGreetings) and bundled sample data/greetings.csv.
• Config — nextflow.config with three profiles:
  • standard — local, no container
  • docker — local, containerized
  • verily_workbench — Google Batch executor, private-address VMs, Workbench VPC/subnet, project and service account pulled from env vars
• Params — test-params.yaml for overriding inputs/outdir.
• Docs — README.md covering local runs, Workbench setup (bucket creation), and running from both the Workflows UI and wb nextflow CLI.

Design notes

• One pipeline, many deploys: same code runs on laptop or Batch; only paths change. Profiles carry the environment differences.
• Task cpus/memory live on the process block (nf-core conf/base.config pattern), not the executor profile; Google Batch sizes the VM from these. Boot disk stays in the
  profile.
• Config via params/env vars, not hardcoded values. outdir/work_dir must be full gs:// paths on Workbench — pipeline fails fast otherwise.
• Public debian:stable-slim image by default; README documents swapping in a private Artifact Registry image.

Commits

• feat(hello-nf-on-vwb): minimal Nextflow-on-Verily-Workbench example
• refactor: task cpus/memory to process block, boot disk in profile (nf-core pattern)
• refactor: rename profile to verily_workbench, params over env vars
• docs/fix: README simplification, drop logsPath, clarify results vs work dir

Test plan

• nextflow run main.nf -profile standard produces results/COLLECTED-greetings.txt
• nextflow run main.nf -profile docker (Docker running)
• wb nextflow run main.nf -profile verily_workbench with gs:// paths
• Register + run from Workflows UI