This imports the contents at a given Path into the tvix store.
It doesn't register the contents at a Path in the store itself, that's up
to the PathInfoService.
Change-Id: I2c493532d65b90f199ddb7dfc90249f5c2957dee
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8159
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
