Fix CocoaPods integration

[radazzouz]

Fixes #21

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Reported in Z#14462

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Details

The current CocoaPods integration is broken. This PR fixes, improves and simplifies the CocoaPods integration. It removes the complex Xcode drag and drop implementation in favor of a much more easier integration.

How to Test:

• Follow the new integration Steps in cocopods.md
• For step for use yarn add https://github.com/PSPDFKit/react-native.git#rad/fix-cocoapods-integration instead of yarn add github:PSPDFKit/react-native

Acceptance Criteria

• The CocoaPods integration works in a newly created app.
• The normal integration works in a newly created app.
• The Catalog sample project works.
• When approved, right before merging, rebase with master and increment the package version in package.json, package-lock.json, and samples/Catalog/package.json (see example commit: 1bf805f).
• Create a new release (and tag) with the new package version (see https://github.com/PSPDFKit/react-native/releases).

[steviki]

LGTM! 👍
Tested it, and it works fine.