v4.0.0

Explicitly replace docker/libtrust with containers/libtrust

• Don't import all of pkg/compression in c/image/types
• update c/storage to v1.13.4
• Simplify Makefile a bit
• Revert "update dependencies"
• Update to mergo v0.3.5
• Add tests for parsing OpenShift kubeconfig files
• add http response to log
• make container tools work with go+openssl
• Update test certificates
• update dependencies
• make test-skopeo: replace c/image module instead of copying code
• copy: don't lose annotations of BlobInfo
• move keyctl to internal & func remove auth from keyring
• media type checks
• Makefeile: use official golang proxy
• update go module
• Replace vendor.conf by go.mod
• internal/testing/explicitfilepath-tmpdir: handle unset TMPDIR
• keyctl: clean up after tests
• copy: fix options.DestinationCtx nil check
• fix cross-compilation by vendoring latest c/storage
• copy: add nil checks
• copy: compression: default to gzip
• vendor.conf: update reference for containers/storage
• compress: define some consts for the compression algos
• copy: use a bigger buffer for the compression
• compression: allow to specify the compression format
• compression: add support for the zstd algorithm