Add Logger protocol and instance and non-instance implementations.

[kevinlind]

Description

Adds:

• Logger protocol in AEPServices which defines methods for logging.
• SDKInstanceLogger implementation of Logger in AEPCore, initialized with an SDKInstanceIdentifier. Each log function uses .instanceAwareName() to include the SDK instance identifier in the log label.
• LoggerImpl in AEPServices which is a base implementation of Logger used in instances where a Logger is needed without an SDKInstanceIdentifier.

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] I have signed the Adobe Open Source CLA.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.