Split tasks to a new repository

[adthrasher]

Finally, we plan to migrate the WDL tools to a new repository. There are several tasks required before we can make the change.

• [ ] Review open PRs on workflows
• [ ] Update documentation (apparently we have a docs/build_for_dnanexus.md that's wildly out of date)
• [ ] Check CI/CD workflows for any needed changes
• [ ] Draft tools-specific README
• [ ] Draft tools-specific contributing guide
• [ ] Update workflows README
• [ ] Choose repository name
• [ ] Choose versioning scheme
• [ ] Move cellranger tasks/workflows to a private repo
• [x] Bring all tools+dependencies up to date