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/proxyblobstore.go

@@ -6,18 +6,21 @@ import (
 	"net/http"
 	"strconv"
 	"sync"
+	"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"
 )
 
 type proxyBlobStore struct {
 	localStore     distribution.BlobStore
 	remoteStore    distribution.BlobService
 	scheduler      *scheduler.TTLExpirationScheduler
+	ttl            *time.Duration
 	repositoryName reference.Named
 	authChallenger authChallenger
 }
@@ -146,7 +149,10 @@ func (pbs *proxyBlobStore) ServeBlob(ctx context.Context, w http.ResponseWriter,
 			return
 		}
 
-		pbs.scheduler.AddBlob(blobRef, repositoryTTL)
+		if pbs.scheduler != nil && pbs.ttl != nil {
+			pbs.scheduler.AddBlob(blobRef, *pbs.ttl)
+		}
+
 	}(dgst)
 
 	_, err = pbs.copyContent(ctx, dgst, w)