Node.js SDK 3: Logging documentation needs additional information covering improvements in logging

In the documentation page for logging for Node.js SDK, https://docs.couchbase.com/nodejs-sdk/3.0/howtos/collecting-information-and-logging.html, we should provide more explanation on the changes and improvements that happened. Things to look into:

• That by default, the SDK will use the default logging function _logToDefault
• Explain how to implement your custom logging function and assign it to the SDK configuration, if a user want's to overwrite the default logging function.
• The mention of "LCB_LOGLEVEL" ... probably need to remove.
• Explain how to send the logging to file if a user wishes to do so.