Fix: Log ruby stdout to console

[njyjn]

Description

This fix allows stdout to be logged to the console, allowing Ruby output operations like logger.info, puts and p to materialize.

Emulates the way sls invoke local --function ... logs such statements.

Motivation and Context

The use of logger is officially supported by AWS in Lambda, and should produce the same result when running offline. It is also useful to be able to print to console for debugging purposes. The implementation of the Python runner does a similar thing.

Resolves #1206

How Has This Been Tested?

I installed and built the local fork into my project and added the following print statements

def handler(event:, context:)
  logger = Logger.new($stdout)

  logger.info('This is a logger.info message')
  p 'This is a p message'
  puts 'This is a puts message'
  ...

Output was

offline: POST /local/hello (λ: hello)
I, [2021-04-14T16:46:02.387705 #74974]  INFO -- : This is a logger.info message
"This is a p message"
This is a puts message
offline: (λ: hello) RequestId: ckni3qx290005qqku6jww556f  Duration: 831.02 ms  Billed Duration: 832 ms
offline: [200] {"statusCode":200,"body":"{\"message\":\"OK\",\"output\":{\"output\":\"hello\"}}"}```

Built locally using package.json and compiled using Babel per the contribution guide.

Please let me know if you have any questions or if there is something I missed. Thanks!

Screenshots (if appropriate):

[icole]

This is awesome, thanks so much for implementing this. I ran in to this the other day as well and put it on the back burner. Definitely +1 to get this merged 👍

[pgrzesik]

Looks good 👍 Thank you @njyjn 🙇