Way to just update relative url() when bundling CSS, don't move file - Propose "update-path" loader command line option

Currently when bundling CSS if you only want to update the relative path in the `url()` and not move the file you have to use the plugin api as in: https://github.com/evanw/esbuild/issues/800.

I'm building a tool for Python/Django developers and my intention is that they will not need to setup a node.js environment to use it[^1]. What I would love would be a built in `update-path` loader, so you could pass an argument to the command line such as `--loader:.png=update-path ` or even better a way to pass a ["ResolveKind"](https://esbuild.github.io/plugins/#resolve-options) to the option, such as `--loader:[url-token]=update-path`.

Using `--external:*.png` is not an option as it does not update the relative path, leaving it as is.

Would something like this be possible?

(P.s. esbuild is incredible!)

[^1]: It will automatically download the correct esbuild binary for their os/platform.

Start with esbuild's plugin API and the command-line loader handling described in the issue, then compare that with the ResolveKind and --external behavior. Done means a built-in update-path loader or equivalent option updates relative url() paths while leaving the referenced files unmoved.

Written by the indexing model from the issue text.