implement webserver

[cgwalters]

This was an original goal. That said I think this may be best as a separate tool that creates a derived/layered image using whatever webserver it wants? That would maximize configurability - users could inject their own branding pages for example.

The core problem here is that the image that will run doesn't currently have the code from this project embedded in it (necessarily). We'd need to inject our own binary into the target, which is absolutely possible but feels kind of unclean.

Well, OTOH that binary won't actually be in the imported ostree commit if injected into /usr/bin/ostree-rs-ext-webserver...so, yeah if it's opt in that may be fine.

[cgwalters]

I'm removing "container exporting ostree on the wire" from the short term roadmap in this project in favor of focusing on container-native flows, e.g. #69 and container deltas.