No more magic separating the metadata from chart tarball - charts are
pushed to registry as a single tarball layer with Chart.yaml in tact.
No more fragile custom symlink chart storage, now following
the OCI Image Layout Specification for chart filesystem cache.
Also:
- Update to ORAS 0.6.0
- Simplify registry client setup with NewClientWithDefaults()
- Remove needless annotations and constants
Fixes#6068Fixes#6141
Signed-off-by: Josh Dolitsky <jdolitsky@gmail.com>