chore: integrate Swift package manager

[thekorn]

recent flutter ships an integration with swift package manager - goal here is no cocoa pods ;)
Also, dependabot would be able to check dependencies of the iOS package as well

https://docs.flutter.dev/packages-and-plugins/swift-package-manager/for-plugin-authors#how-to-add-swift-package-manager-support-to-an-existing-flutter-plugin