Initial working GitHub action

Updating a lambda from an S3-hosted zip file works when providing each required value:

• LAMBDA_NAME
• AWS_S3_BUCKET
• AWS_S3_KEY
• AWS_ACCESS_KEY_ID
• AWS_SECRET_ACCESS_KEY
• AWS_REGION

Not all options of update-function-code are yet supported. Of specific note, these options are not yet enabled:

--publish 	Creates new version of the function
--revision-id	Prevents modification of changed-since-read function