feat(aws/lambda): Add update lambda stage.

[andrewbackes]

CRUD operations for lambdas are already available in Clouddriver here. This stage allows users access to the update lambda operation from within a pipeline.

Usage

After you have Lambda enabled in Clouddriver, you can hit Orca with something like:

curl -X POST \
  http://localhost:8083/orchestrate \
  -H 'Content-Type: application/json' \
  -d '
  {
      "application": "myapp",
      "description": "updateLambda Test",
      "stages": [
        {
            "type": "updateLambdaFunction",
            "region": "us-west-2",
            "functionName": "arn:aws:lambda:us-west-2:<acct>:function:<function-name>",
            "description": "sample",
            "credentials": "aws-acct",
            "handler": "lambda_function.lambda_handler",
            "memory": 512,
            "role": "arn:aws:iam::<acctno>:role/service-role/test",
            "runtime": "python3.6",
            "timeout": "68",
            "tags": [{"key":"value"}]
        }
      ] 
  }
'

Edit: Added usage instructions