metacache: Add option for life extension (#10837)

Add `MINIO_API_EXTEND_LIST_CACHE_LIFE` that will extend 
the life of generated caches for a while.

This changes caches to remain valid until no updates have been 
received for the specified time plus a fixed margin.

This also changes the caches from being invalidated when the *first* 
set finishes until the *last* set has finished plus the specified time 
has passed.

cmd/handler-api.go

@@ -33,6 +33,7 @@ type apiConfig struct {
 	requestsPool     chan struct{}
 	clusterDeadline  time.Duration
 	listQuorum       int
+	extendListLife   time.Duration
 	corsAllowOrigins []string
 }
 
@@ -65,6 +66,7 @@ func (t *apiConfig) init(cfg api.Config, setDriveCount int) {
 	t.requestsPool = make(chan struct{}, apiRequestsMaxPerNode)
 	t.requestsDeadline = cfg.RequestsDeadline
 	t.listQuorum = cfg.GetListQuorum()
+	t.extendListLife = cfg.ExtendListLife
 }
 
 func (t *apiConfig) getListQuorum() int {
@@ -74,6 +76,13 @@ func (t *apiConfig) getListQuorum() int {
 	return t.listQuorum
 }
 
+func (t *apiConfig) getExtendListLife() time.Duration {
+	t.mu.RLock()
+	defer t.mu.RUnlock()
+
+	return t.extendListLife
+}
+
 func (t *apiConfig) getCorsAllowOrigins() []string {
 	t.mu.RLock()
 	defer t.mu.RUnlock()