fix: better Carthage support

[crleona]

Summary

Carthage support has a few issues that need to be resolved:

• As of Carthage 0.37.0, Carthage will build all subprojects in a dependency, which means it includes our sample apps. Our ObjC sample app is currently broken on the latest versions of Xcode as you are no longer allowed to reference a package that is a direct ancestor of the project. I converted this to a direct project reference instead, and enabled emitting a module to keep the same semantics.
• analytics-connector-ios needs to be added as a dependency in a Cartfile, similar to https://github.com/amplitude/Amplitude-iOS/blob/main/Cartfile. This resolves #139 .

Checklist

• [X] Does your PR title have the correct title format?
• Does your PR have a breaking change?: No

[github-actions[bot]]

:tada: This PR is included in version 1.4.2 :tada:

The release is available on:

• GitHub release
• v1.4.2

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