chore: de-duplicate fuse mounting/unmounting code

[dtrudg]

Type of issue

technical debt

Description of issue

Following work on the OCI mode, we now have internal/pkg/util/fs/fuse as a place for FUSE mount/unmount related code.

We are performing FUSE mounts in various other places, using different code.

We should expand internal/pkg/util/fs/fuse so that it can be used to replace other FUSE mount/unmount code, to reduce the number of unique places that may need to be examined given any FUSE mount bugs / maintenance.