Add `SOCKET_MODE`, `SOCKET_USER` and `SOCKET_GROUP` in addition to `SOCKET_PATH` to adapter-node

Describe the problem

I'm struggling with sharing sveltekit app's socket with a web server.

Describe the proposed solution

Most daemons nowadays allow you to customize socket permissions and ownership via flags. Add SOCKET_MODE, SOCKET_USER and SOCKET_GROUP environment variables

Alternatives considered

One way would be to add web server to the app's linux group but that way the web server will be able to read more than just the socket.

Importance

would make my life easier

Additional Information

Looks like adapter-node uses polka to serve http requests.

https://github.com/sveltejs/kit/blob/0afc71d936821b45ed4987b9bb7c7af9e826c3a9/packages/adapter-node/src/index.js#L41

Which uses nodejs's http server.listen function which accepts the path to unix socket to create it

https://nodejs.org/docs/v22.19.0/api/net.html#serverlistenoptions-callback

I couldn't find any info on how to change permission/ownership for it. I did try to change ownership and permissions manually after starting the app but it keeps resetting it.

Start in packages/adapter-node/src/index.js around the referenced server.listen call, then read Node.js net.Server.listen options documentation. Trace how SOCKET_PATH is handled and determine how the three requested environment variables should map to Unix socket permissions and ownership. Done means adapter-node supports the variables without regressing existing socket behavior.