Improve http api for large cluster deployment environments to make it more friendly

[maxjiang153]

see: https://github.com/comfyanonymous/ComfyUI/issues/2401

Add a new instance id generated while server bootstrapping to help identify instances in a cluster environment.

Add the ComfyUI-instance-id http header to make http api identifiable in a cluster environment.

Add server instance id and prompt queue remaining task count field to make it show more runtime informations