This PR fixes a bug in sync, in which desinations for synced files were
being calculated incorrectly. For the hot-reload example, app.py was
being synced to /src/app.py instead of /app.py, so it appeared as if
sync wasn't actually working.

To fix this issue, I fixed a bug in the intersect function to make sure
destination calculation follows the Docker COPY command rules.

For example, we had a unit test as follows:

syncMap: **/**/*.js": "."
file: dir1/dir2/node.js
dst: /dir1/dir2/node.js

when the destination should actually be /node.js based on Docker COPY
command rules.

since go-containerregistry can't currently handle both