Make our own logger; add API endpoints to query/clean log file

[njparadis]

Setup a Logger class to log out to out own klaviyo.log file under /var/log Replaced instances where we use the built-in Magento logger with our own

TODO:

• Appropriate permissions level for the API endpoint (I think Magento_Backend::Admin but need to research)
• Expand the stuff we log out
  • Newsletter subscriptions?
  • Newsletter unsubscribes?
  • Other exceptions?
• Figure out how to retrieve the log file contents in the getLog() function

[njparadis]