Improve Sandbox Extensions

Summary The [sandbox extensions]( are very limited. Some features would be helpful: • Change the name of the endpoint with an id, like the ["normal" endpoint extension]( • Allow sending extra [headers]( for SandboxEndpointResponse Basic Example See Detailed Design Motivation I tought it would be pretty cool to serve an SPA via directus. It already serve the admin dashboard, express should be capable of serving another SPA as well. So I created an [extension]( which works basically. But I ran into some issues serving an SPA: 1. I had to rename my npm package because the sandbox endpoint uses the name from package.json 2. I tried to serve my files but run into an issue were I need to set the mimeType inside the headers for .js files Detailed Design 1. Sandbox Endpoint id 1. Add id: z.string() to this [line]( 2. Inside this [line]( it should check for extension.sandbox?id ?? extension.name. > Note: It can be name or endpointName insta…