Option to configure proxy cache TTL

Currently when registry is run as proxy it tries to cleanup unused blobs
from its cache after 7 days which is hard-coded. This PR makes that
value configurable.

Co-authored-by: Shiming Zhang <wzshiming@foxmail.com>
Co-authored-by: Manish Tomar <manish.tomar@docker.com>
Signed-off-by: Shiming Zhang <wzshiming@foxmail.com>

registry/proxy/proxymanifeststore.go

@@ -4,22 +4,21 @@ import (
 	"context"
 	"time"
 
+	"github.com/opencontainers/go-digest"
+
 	"github.com/distribution/distribution/v3"
 	dcontext "github.com/distribution/distribution/v3/context"
 	"github.com/distribution/distribution/v3/reference"
 	"github.com/distribution/distribution/v3/registry/proxy/scheduler"
-	"github.com/opencontainers/go-digest"
 )
 
-// todo(richardscothern): from cache control header or config
-const repositoryTTL = 24 * 7 * time.Hour
-
 type proxyManifestStore struct {
 	ctx             context.Context
 	localManifests  distribution.ManifestService
 	remoteManifests distribution.ManifestService
 	repositoryName  reference.Named
 	scheduler       *scheduler.TTLExpirationScheduler
+	ttl             *time.Duration
 	authChallenger  authChallenger
 }
 
@@ -77,7 +76,10 @@ func (pms proxyManifestStore) Get(ctx context.Context, dgst digest.Digest, optio
 			return nil, err
 		}
 
-		pms.scheduler.AddManifest(repoBlob, repositoryTTL)
+		if pms.scheduler != nil && pms.ttl != nil {
+			pms.scheduler.AddManifest(repoBlob, *pms.ttl)
+		}
+
 		// Ensure the manifest blob is cleaned up
 		// pms.scheduler.AddBlob(blobRef, repositoryTTL)