Adds type to package.json for use when running npm init.

1. Defaults to commonjs
2. Validates against commonjs | module
3. Allows npm init --init-type module -y
4. Allows for init.type=module in .npmrc
5. Improved tests to make it easier to manage removing / adding new prompts

on the shoulders of #302
a part of the npm 11 roadmap npm/statusboard#898
statusboard issue here npm/statusboard#654
older rfc npm/rfcs#347

Note: Running npm init --init-type=module -y will not overwrite an existing package.json type field. This is deemed out of scope for init. To update an existing type edit it manually or field, use jq '.type = "module"' package.json > tmp.json && mv tmp.json package.json.