Switch to Stripe SPM SDK to speed up CI/CD pipelines

[nbeadman]

Package.swift includes a dependency:

    dependencies: [
        .package(url: "https://github.com/stripe/stripe-ios.git", exact: "23.27.3")
    ],

to the official Stripe SDK. However, because Swift Package Manager checks out the entire git repo, this takes a significant amount of time. To mitigate that issue Stripe provides a much lighter weight repo with the same releases at: https://github.com/stripe/stripe-ios-spm with the same tagged releases. Changing the dependency to that repo will speed up compilation within our CI/CD pipeline.