Add ability to subscribe to multiple log groups

[stuft2]

Currently I am manually triggering the subscription lambda for each log group. I would like the ability to subscribe to multiple log groups without having to manually trigger the lambda. This would involve changing the subscription lambda event to allow an array of log group prefixes:

{
  "detail": {
    "requestParameters": {
      "logGroupNames": [
        "EXAMPLE"
      ]
    }
  }
}

Similar to #38

[stuft2]

@Suzanna-Volkov do you have thoughts on supporting this method of subscribing to log groups?