Enhance forms with loading and error states

[devidw]

I think it would be great to have loading indicators in the forms will the request is processed and also have the form fields disabled in the meantime.

Also, when there is an error, it would be great when the server actions would return the error details for frontend notices.

I totally understand, when you don't want to have all of this implemented here, to keep things simple and related to pocketbase only.

However, when you also think this would be nice to have (should not be that much boilerplate), then I could open a PR for those features.

What do you think? @jianyuan