feat: Logging interface for SDK

[jnewc]

What this PR does

• Introduce a logging interface that can be implemented by merchants
• Implements it within the debug app

QA

• I manually tested this with a demo application (simulator)
• I manually tested this with a demo application (real device)
• I wrote unit tests for each new util-like function
• I wrote at least basic e2e tests for the new functionalities or new paths

Documentation

• If this PR modifies the API, I updated the API Reference.
• If this PR adds new options to the API, I wrote some documentation or guide in the online documentation

After merging

• Make sure a new release has been pushed to Cocoapods trunk

[github-actions]

	Warnings
⚠️	> Pull Request size seems relatively large. If this Pull Request contains multiple changes, please split each into separate PR will helps faster, easier review.
⚠️	Please assign someone aside from CODEOWNERS (@checkout-pci-reviewers) to review this PR.

Generated by 🚫 Danger Swift against fc37644

[borisprimer]

LGTM! 👍

[borisprimer]

LGTM! Great work!

[semirp]

General question, if developer only use headless integration, is it enough to set Logger only on Primer object?

[jnewc]

General question, if developer only use headless integration, is it enough to set Logger only on Primer object?

Yes, the logger works independently of checkout type. This is why the logger property is on the SDK singleton (Primer.shared.logger)