Skip devDependencies in deploy build step

[aduth]

Why: We should not need to install devDependencies in deployed environments, as they should not expect to be needed for build or for runtime. This may improve build time by reducing dependency preparation time, and avoid imposing requirements on deployed environments for dependencies which are only relevant for development (see #4680).

Status: Currently for testing. May not be mergeable, pending:

1. Need to audit existing dependencies to make sure they're categorized correctly
   • Then update dependencies documentation to remark that the distinction is meaningful for build
2. May want to change how we build and deploy IDP artifacts (assets, etc). See related Slack discussion.
3. May want to consider setting up CircleCI to match this behavior except when running JavaScript tests, which may require breaking up the existing build task.

[aduth]

I think we only need an active branch for testing, so I'll close the pull request and keep the branch alive. If this looks promising, we can reopen the pull request.