add --no-download flag to dvc import-url/dvc update to only create/update .dvc
files without downloading the associated data.
Created .dvc files can be fetched using `dvc pull` or can be
updated using `dvc update --no-download`.
`fetch_all_exp()` in `clone()` was called with `url="origin"`, which
resulted in the operation being performed with the remote URL defined
in the cloned repo's config, which did not include any credentials
initially provided to clone.
Fixes#7670
When staging a directory, always save a "raw dir object" to the odb.
If the corresponding ".dir" object has not been added to the odb,
`stage()` calls can load the tree from the raw dir object instead of
rebuilding it by walking the directory.
This can lead to significant speed improvements when calling
`dvc status` for modified directories.
Fixes#7390
Daniele Trifirò