feat(AWSCore): Upgrading CocoaLumberjack to version 3.8.4

[sebaland]

Description of changes

This PR upgrades the CocoaLumberjack fork within AWSCore (called AWSCocoaLumberjack) to version 3.8.4.

I've also updated the README to use AWSDDOSLogger instead of AWSDDTTYLogger in our logging example.

Additional Changes

The following has been made for backwards compatibility:

• Addition of the logLevel property in AWSDDLog, so that customers can easily set the global log level.
• AWSDDTTYLogger.sharedInstance is explicitly marked as nullable, but the id<AWSLogger> arguments in [AWSDDLog add:] and [AWSDDLog add:withLevel:] have been explicitly marked as non-null. This is technically a breaking change for Swift customers, so I've added a Swift extension that offers methods that take optionals, but are deprecated and instruct to not use optionals
  • ⚠️ Note: The actual behaviour has not changed. In the old version, AWSDDTTYLogger.sharedInstance could still return nil and then it would just be ignored by [AWSDDLog add:] and [AWSDDLog add:withLevel:].

Check points:

• Added new tests to cover change, if needed
• All unit tests pass
  • https://github.com/aws-amplify/aws-sdk-ios/actions/runs/8102383487
• All integration tests pass
  • https://github.com/aws-amplify/aws-sdk-ios/actions/runs/8102383486
• Updated CHANGELOG.md
• Documentation update for the change if required
• PR title conforms to conventional commit style

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.