[📖] onSubmitCompleted$ Event Handler

[thejackshelton]

Suggestion

From what I see there isn't any documentation covering the onSubmitCompleted$ event handler. This was the perfect solution to the problem I was having, and the person who recommended it to me found it in the type definitions.

I can see in VSCode a description now of what it does: "Event handler executed right after the action is executed successfully and returns some data."

Although for many others I think it would be very beneficial to have this in the docs.

Relevant conversation in the discord: https://discord.com/channels/842438759945601056/1095037577435824210/1095037577435824210

If there's anything I can do that would contribute to that documentation would love to hear it. Should I make a PR about it and include it in a subsection on the route action/form action page?