Allow plugin code and icons to be resolved relative to the manifest file for easier plugin hosting and management, especially in containerized environments.
### Is your feature request related to a problem? Please describe. I have setup penpot using podman and now wanted to explore hosting plugins. I setup a container with nginx and one of the plugins provided in the repo (I use pnpm build and copy the dist output to the image). One container works fine. Now I wanted to expand it to multiple so I created one image per plugin (nginx + plugin dist). Then a used another nginx container to proxy_pass to the internal network. Everything should be fine on the container side. When I try to load a plugin it cannot resolve the icon and plugin.js. ### Describe the solution you'd like. Allow assets and code to resolved relative to the manifest path. Currently this is not possible because the frontend store set plugin manifest host to the origin. Line 88. <https://github.com/penpot/penpot/blob/52496243ac83409acb71a82adcec2fca113932fa/frontend/src/app/plugins/register.cljs#L81-L91> ### Describe alternatives you've considered. - Exposing each