chore: adds example projects for CocoaPods and SPM

[fadi-george]

Description

One Line Summary

This is part 1 of the spm changes, this just more example projects for testing.
Doesn't need thorough review.

Details

Motivation

Demonstrates the setup of the OneSignal Flutter plugin using both CocoaPods and Swift Package Manager for iOS projects.
This provides developers with clear examples for integrating the plugin into their projects using their preferred dependency management tool.

Scope

• Adds example_pod configured for CocoaPods.
• Adds example_spm configured for Swift Package Manager.
• Includes necessary files and configurations for both iOS and Android platforms within each example.
• Sets up a basic Flutter app in each example to showcase the plugin's functionality.

Testing

Manual testing

Tested the creation of the example projects and verified their basic structure.
Confirmed that the necessary files and configurations are present for both CocoaPods and SPM integration.

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
  • If it is hard to explain how any codes changes are related to each other then it most likely needs to be more than one PR
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
  • Simplify with less code, followed by splitting up code into well named functions and variables, followed by adding comments to the code.
• I have reviewed this PR myself, ensuring it meets each checklist item
  • WIP (Work In Progress) is ok, but explain what is still in progress and what you would like feedback on. Start the PR title with "WIP" to indicate this.

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This change is 

[nan-li]

Are we planning to keep all 3 examples after we finish testing and merging spm changes?

[fadi-george]

Are we planning to keep all 3 examples after we finish testing and merging spm changes?

I'd keep them around for now, I'd say its no harm since they don't get bundled anyway.