No explict ways to tell the wasm runtime what file and directory wasm binary has access to

This is from a discussion at the CG meeting this week. Runwasi currently has no ways to specify, explicitly, what file and directories a wasm container have access to.

_Originally posted by @Mossaka in https://github.com/containerd/runwasi/pull/142#discussion_r1240183875_

Start by reading the discussion linked from this issue, especially the original discussion in containerd/runwasi#142. Trace how runwasi currently exposes filesystem access to wasm containers. Done means defining and implementing an explicit way to specify which files and directories a wasm binary may access.

Written by the indexing model from the issue text.