Settings.app Acknowledgements.plist is missing?

Good afternoon, I'm using Bazel and `rules_apple` to compile an iOS app and more 👍

I've got several third party dependencies. For attribution, I'd like to expose the licenses to users in `Settings.app`

Is there a way to generate this for all of my deps? I noticed that `objc_library` ( and all other build rules ) are supposed to have `licenses` as an attribute.

It wasn't clear to me if this is supported in iOS and I couldn't find anything related in `rules_apple` or the [docs](https://bazel.build/versions/master/docs/be/functions.html#licenses). Previously, this plist was governed by with CocoaPods, which [automatically generates](https://guides.cocoapods.org/syntax/podspec.html#license) this plist, and sets up the bundle. It'd be awesome if Bazel had this ability!

Start with Bazel's licenses attribute documentation and the rules_apple build rules, including objc_library, to determine whether dependency license metadata is available to iOS bundles. Done means defining and documenting a supported way to generate and include Settings.app's Acknowledgements.plist for all dependencies.

Written by the indexing model from the issue text.