implement volume mounts, env, and args

[bacongobbler]

The wasmtime provider allows volumes, environment variables, and function arguments to the main program. We have that available, but it's currently stubbed out/unused.

krustlet-wasm3/src/wasi_runtime.rs

Lines 52 to 58 in 9f4faa3

	env: HashMap<String, String>,
	/// the arguments passed as the command-line arguments list
	args: Vec<String>,
	/// a hash map of local file system paths to optional path names in the runtime
	/// (e.g. /tmp/foo/myfile -> /app/config). If the optional value is not given,
	/// the same path will be allowed in the runtime
	dirs: HashMap<PathBuf, Option<PathBuf>>,