Normalize the paths between the configuration file and module source about spin

[radu-matei]

The current implicit assumption is that the module source is relative to spin.toml, and I think the newly introduced ApplicationOrigin structure in the configuration should help with this —

spin/crates/config/src/lib.rs

Lines 130 to 135 in ec5a000

	/// The location from which an application was loaded.
	#[derive(Clone, Debug)]
	pub enum ApplicationOrigin {
	/// The application was loaded from the specified file.
	File(PathBuf),
	}

I'd start with implicit relative vs. absolute path (i.e. "if it starts with /), and stay away of the file scheme for now. We could add it later if we think it's a use case we want to support.

[michelleN]

Should we make it so that the path must be relative to the directory that the Spin.toml file lives? What happens if the user wants to specify absolutely path?

Right now I'm thinking.. if component source is a path, check if it is relative or not. Relative paths are relative to the directory where the Spin.toml file lives. If not relative, use absolute path given. How should a user denote they're supplying an absolute path? Should it be by using / at the beginning of the component source string? Should they specify the file URI scheme? https://en.wikipedia.org/wiki/File_URI_scheme