Add function invoking ability to ofn cli

[benjaminhuo]

In the ofn cli, we can add function invoking ability like lambda:

• Trigger a sync function:

aws lambda invoke --function-name my-function --payload '{ "key": "value" }' response.json

output

{
    "ExecutedVersion": "$LATEST",
    "StatusCode": 200
}

• Trigger an async function: To invoke a function asynchronously, set the invocation type parameter to Event.

aws lambda invoke \
  --function-name my-function  \
      --invocation-type Event \
          --cli-binary-format raw-in-base64-out \
              --payload '{ "key": "value" }' response.json