Feature Request: Specify ComfyUI Version

[Pseudotools]

Forgive me if I've missed it - but it doesn't look like we have a way of specifying a particular version of ComfyUI. The default version used here looks like it's from last September, and I know we can set AUTO_UPDATE env variable to update to the latest version, but it doesn't look like we can set a particular ComfyUI tag to build from.

Request: add an environment variable that sets the tag of the desired ComfyUI version.

And of course, thank you so much for this excellent Docker image!