builder-next/prune: Handle "until" filter timestamps

Fixes `docker system prune --filter until=<timestamp>`.
`docker system prune` claims to support "until" filter for timestamps,
but it doesn't work because builder "until" filter only supports
duration.
Use the same filter parsing logic and then convert the timestamp to a
relative "keep-duration" supported by buildkit.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

api/swagger.yaml

@@ -8226,7 +8226,7 @@ paths:
 
             Available filters:
 
-            - `until=<duration>`: duration relative to daemon's time, during which build cache was not used, in Go's duration format (e.g., '24h')
+            - `until=<timestamp>` remove cache older than `<timestamp>`. The `<timestamp>` can be Unix timestamps, date formatted timestamps, or Go duration strings (e.g. `10m`, `1h30m`) computed relative to the daemon's local time.
             - `id=<id>`
             - `parent=<id>`
             - `type=<string>`

builder/builder-next/builder.go

@@ -14,6 +14,7 @@ import (
 	"github.com/containerd/containerd/remotes/docker"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/backend"
+	timetypes "github.com/docker/docker/api/types/time"
 	"github.com/docker/docker/builder"
 	mobyexporter "github.com/docker/docker/builder/builder-next/exporter"
 	"github.com/docker/docker/builder/builder-next/exporter/overrides"
@@ -626,11 +627,16 @@ func toBuildkitPruneInfo(opts types.BuildCachePruneOptions) (client.PruneInfo, e
 	case 0:
 		// nothing to do
 	case 1:
-		var err error
-		until, err = time.ParseDuration(untilValues[0])
+		ts, err := timetypes.GetTimestamp(untilValues[0], time.Now())
 		if err != nil {
-			return client.PruneInfo{}, errors.Wrapf(err, "%q filter expects a duration (e.g., '24h')", filterKey)
+			return client.PruneInfo{}, errors.Wrapf(err, "%q filter expects a duration (e.g., '24h') or a timestamp", filterKey)
 		}
+		seconds, nanoseconds, err := timetypes.ParseTimestamps(ts, 0)
+		if err != nil {
+			return client.PruneInfo{}, errors.Wrapf(err, "failed to parse timestamp %s", ts)
+		}
+
+		until = time.Since(time.Unix(seconds, nanoseconds))
 	default:
 		return client.PruneInfo{}, errMultipleFilterValues{}
 	}