Feature request: Write access for plugins?

[allmarkedup]

As suggested in #15:

"It also might be interesting to consider if there's merit in a standard pattern for plugins to feed data back into a running Fractal server instance. This could be pretty simple, e.g. allowing plugins to register for a hook, and then providing an endpoint that accepts (say) something like a component handle, a plugin handle and an arbitrary payload that is received by the plugin fn registered to the hook.

A couple of example workflows that I can think of that could make use of something like this:

Design review: Our design team will often use our Fractal instances to design review components while they're in dev. It would be great to be able to update component metadata / config to store data about that process in the component's config file, e.g. storing a timestamp or updating component status after a designer has hit a "complete review" button in the fractal UI.

In-browser prop editor: Being able to fiddle about with prop values live in the browser a la Storybook Knobs would be great, but to get it working for SSR templates like Twig you would need a way to tell Fractal to re-render a given component with a revises set of prop values. See also my FR for typed props or similar below.

To be clear, I'm suggesting Fractalite should just provide the hook for plugins to register on and endpoint to invoke the hook, and leave everything else to plugins."