Make WASI preopened_dir more configurable

[Mossaka]

          I believe this is the way it's done today but in the case of the OCI layers I don't think we need these permissions.  Any thoughts on how we can make this more configurable?  It feels like this is where a OCI artifact with configuration that had info like this in it would come into play

Originally posted by @jsturtevant in #401 (comment)

[lengrongfu]

/assign

[lengrongfu]

@Mossaka Can you give me some suggestions?

preopened should how to config, we should use env or flags or config file to config it? now look like need to change https://github.com/containerd/rust-extensions this project.

[Mossaka]

I think the discussion from that PR was that we may add a config file as a OCI layer, but we haven't figured out if that's the route we want to go with. ping @jsturtevant for more context here.

[lengrongfu]

cc @justincormack can you provide more info?

[jsturtevant]

@lengrongfu I don't think we have a clear idea of how we plan to handle this at this point. This is on the table for discussion at the OCI sub-group in the wg-wasm cncf group. If you have some thoughts or would like to listen in we are meeting next week Tue Feb 27th 8:00am - 9:00am (PST) (search for wasm on https://www.cncf.io/calendar/)