iOS - Specify which fields couldn't be automatically populated during `variants init`

[arthurpalves]

Background

When running variants init for an iOS project (automatically detected or specified with --platform ios), the tool already tries to populate variants.yml with project information, such as name, bundle id etc. In some cases, not all the placeholders can be replaced automatically, resulting in:

This isn't a problem, as variants.yml should/can be modified manually at this point.

Enhancement

Specify exactly which fields couldn't be populated, so that it's easier to visualize what needs attention in the YAML spec.

Example:

 ⚠️ We were unable to populate the following fields in the `variants.yml` spec.
 Please add them manually by replacing the placeholders:
     * ios.targets.FooTarget.name
     * ios.targets.FooTarget.source.path
     [...]

[arthurpalves]

@mausvargas does this proposal satisfy your use case?