Simplify Integration Interface

Simplify Integration Interface:

• Created separate interfaces: Integration and Logger
  • Also created a specific Integration interface, called ExternalIntegration for non-wiki sites
• Moved logWarning from Integration to Logger interface
• Removed old functions from Integration interface: getCurrentUserExperiments and isCurrentUserEnrolled
• Removed some functions from Integration interface:
  • getPageviewId and getSessionId because that can be done via getContextAttributes() in the corresponding implementation
• Removed unused function setContextAttributes from DefaultIntegration (it wasn't defined in the Integration interface either) and it seems they are not needed. Contextual attributes are filled via getContextAttributes when implementation the Integration interface in the corresponding platform
• Related tests have been updated (unit + integration)

Bug: T359618