Allow messaging to & from the iFrame's internal window

### Description

I the predecessor (Dashboard 1.0) iFrame node, when sending `msg.payload` to the node it would stringify & post it to the internal window. for example, when playing a YouTube video in the iFrame, you could control it with messages such as:
```
msg.payload = {
event: "command",
func: "pauseVideo",
args: []
}
```
This was done as follows:
`iframe.contentWindow.postMessage(JSON.stringify(msg.payload), origin);
`

It would be good to have this functionality here too. Also, would be good to add listener and an output port and, and support receiving messages from the iFrame's internal window,

### Have you provided an initial effort estimate for this issue?

I can not provide an initial effort estimate