manifest, push: implement --replicate with compression

This is a proof-of-concept PR and needs few upstream PR from `c/image`.

Proof of concept PR to demonstrate and new API added in `c/image`.
Adds a new flag `--replicate <compression>` to `manifest push`, which when added
will push exisiting manifest on host while replicating the instances
with required `compression`.

Example usage

```console
./buildah manifest create localhost:5000/list:latest
./buildah build -t test .
./buildah manifest add localhost:5000/list:latest test
./buildah manifest push --tls-verify=false --all --replicate zstd localhost:5000/list:latest
```

Signed-off-by: Aditya R <[email protected]>

cmd/buildah/manifest.go

@@ -221,6 +221,7 @@ func init() {
 	flags.StringVar(&manifestPushOpts.creds, "creds", "", "use `[username[:password]]` for accessing the registry")
 	flags.StringVar(&manifestPushOpts.digestfile, "digestfile", "", "after copying the image, write the digest of the resulting digest to the file")
 	flags.StringVarP(&manifestPushOpts.format, "format", "f", "", "manifest type (oci or v2s2) to attempt to use when pushing the manifest list (default is manifest type of source)")
+	flags.StringSliceVar(&manifestPushOpts.replicateWithCompression, "replicate", nil, "replicate instances with selected compression while pushing")
 	flags.BoolVarP(&manifestPushOpts.removeSignatures, "remove-signatures", "", false, "don't copy signatures when pushing images")
 	flags.StringVar(&manifestPushOpts.signBy, "sign-by", "", "sign the image using a GPG key with the specified `FINGERPRINT`")
 	flags.StringVar(&manifestPushOpts.signaturePolicy, "signature-policy", "", "`pathname` of signature policy file (not usually used)")
@@ -897,6 +898,7 @@ func manifestPush(systemContext *types.SystemContext, store storage.Store, listI
 		RemoveSignatures:   opts.removeSignatures,
 		SignBy:             opts.signBy,
 		ManifestType:       manifestType,
+		ReplicateWithCompression: opts.replicateWithCompression,
 	}
 	if opts.all {
 		options.ImageListSelection = cp.CopyAllImages

cmd/buildah/push.go

@@ -46,6 +46,7 @@ type pushOptions struct {
 	encryptionKeys     []string
 	encryptLayers      []int
 	insecure           bool
+	replicateWithCompression []string
 }
 
 func init() {