As all CLI input is considered to be string, eg. a
"npm install --lockfile-version 3" would fail with the error messages:

```
npm WARN invalid config lockfile-version="3" set in command line options
npm WARN invalid config Must be one of: null, 1, 2, 3
```

Until we have a config system that supports setting type and possible values
of configs, we have to specify all string and number values for the
`lockfile-version`, but we coerce all values to numbers in the flattener.

Co-authored-by: @voxpelli
Co-authored-by: @isaacs

PR-URL: #3949
Credit: @lukekarrys
Close: #3949
Reviewed-by: @isaacs

PR-URL: #3943
Credit: @wraithgar
Close: #3943
Reviewed-by: @lukekarrys

PR-URL: #3953
Credit: @lukekarrys
Close: #3953
Reviewed-by: @nlf