v5.18.0

• Add copy.Options.PreserveDigests
• Link the two variants of cannotModifyManifest*Reason together.
• shortnames: mechanism to enforce resolving to Docker Hub
• manifest.GuessMIMEType(): recognize self-described OCI manifests
• Add a comment about only looking up credential helpers by registry
• Reorganize the success case in getCredentialsWithHomeDir
• Introduce a string key in getCredentialsWithHomeDir
• Modify findAuthentication to use a string key instead of a reference.Named
• Allow using namespaced keys in GetCredentials and GetAuthentication
• Rename useLegacyAPI to useLegacyFormat
• Fix GetAllCredentials
• Reject invalid keys in GetCredentials/GetAuthentication
• Make validateKey a bit more strict
• Don't include full manifest contents in error messages
• Log if a manifest upload doesn't contain a Docker-Content-Digest header
• docker/config: handle credentials not found errors
• docker: less bears :(
• Remove unused filler argument to customPartialBlobCounter
• Inline decor.Any into the caller
• Inline sstyle into the only user
• Simplify a check for missing credentials
• Fix handling of missing data in GetAllCredentials
• Fix the pseudo-version of github.com/opencontainers/image-spec
• Update golang.org/x/crypto, and silence warnings about openpgp