[Feature] allow path to a directory containing a manifest or a manifest as a Config::server()

[mrcjkb]

luarocks allows you to pass a directory containing a manifest (or a path to a manifest, I don't recall) as a --server.
This can be useful for local debugging. We should support it too.

[vhyrro]

I don't like having too many flags but --local-server could be a nice way of fragmenting the code to prevent spaghetti? Then we can add a parser to clap to ensure that --server is a well-formed URI. I always hated luarocks's "do everything in one go" approach to the CLI.

[mrcjkb]

I like the idea.

Edit - Thought: a well-formed URI can also be file://.... How would we handle that?