External link local icon support

[duhmojo]

Is your feature request related to a problem? Please describe.
The external link support is a bit frustrating because the icon must be external from Casa and you don't offer file public sharing (e.g. I upload a png to a folder, share it, then use the link in the external link icon field), the option to upload an image for the external link icon, or simply support for me to set an internal file path to the icon (e.g. right click the file in Files, copy path, paste link into external link icon field, like /DATA/Documents/icons/adguard-home-icon-507x512-ovjn0dm6.png or file:.///DATA/Documents/icons/adguard-home-icon-507x512-ovjn0dm6.png)

Many people, I'm sure, use Casa in part as a dashboard for easily linking to other local services, either hosted on the same IP or another, in a container or outside.

I tried using Casa for simple container management but it was too limiting and the container App Store integration isn't as seamless or perfect as needed to be fool proof e.g. ports changing, having no clue what was installed after selecting the app, etc... Instead I setup simple LXC images in my Proxmox separate from Casa and added their UIs as External Links in Casa. AdGuard in particular is frustrating in Casa because the App port is the Wizard/Setup port, after AdGuard is setup it listens on a different port and your App doesn't change to match it. So clicking will give a "Page not found". Further you don't support macvlan for containers if I create a custom docker network for it, to allow for the AdGuard DHCP service. I don't expect you to fix the AdGaurd integration, this only serves as proof that good External Link support is needed because in many cases you can't possibly control, the App integration will be too limiting. Make sure External Links and your great File support work more flexibly.

Describe the solution you'd like
Any of the following in order of preference:

1. External Link icon field supports upload image for icon support.
2. External Link icon field supports browsing to existing image in Files.
3. External Link icon field supports pasting a File right click Copy Link path, with or without file:// as the designation this is a local file, not a url.
4. Saving an External Link will download the icon field URL image locally, then serve it instead of the remote URL.

Describe alternatives you've considered
Tried extracting the File URL via networking but you are using a token prop in the URL that'll change every login. I could also host a HTTP server but then I have to host yet another container for Casa to access a simple png.

Additional context
Add any other context or screenshots about the feature request here.