[VOL-3860] redis client support in voltha-lib-go

redis client support has been added in this patch. There are two
types client `redis` and `redis-sentinel` to connect a redis instance.
redis-sentinel is required to be able to find the master redis
instance from a redis-sentinel process. See redis-sentinel usage
https://redis.io/topics/sentinel and
https://pkg.go.dev/github.com/go-redis/redis/v8#NewFailoverClient
for more information. If there is no need to have any failover
mechanism then the redis client type is the option to choose.

Change-Id: I997ed92115a9d565df632c6dd8184b9bab77b991
diff --git a/vendor/github.com/go-redis/redis/v8/cluster_commands.go b/vendor/github.com/go-redis/redis/v8/cluster_commands.go
new file mode 100644
index 0000000..1f0bae0
--- /dev/null
+++ b/vendor/github.com/go-redis/redis/v8/cluster_commands.go
@@ -0,0 +1,25 @@
+package redis
+
+import (
+	"context"
+	"sync/atomic"
+)
+
+func (c *ClusterClient) DBSize(ctx context.Context) *IntCmd {
+	cmd := NewIntCmd(ctx, "dbsize")
+	var size int64
+	err := c.ForEachMaster(ctx, func(ctx context.Context, master *Client) error {
+		n, err := master.DBSize(ctx).Result()
+		if err != nil {
+			return err
+		}
+		atomic.AddInt64(&size, n)
+		return nil
+	})
+	if err != nil {
+		cmd.SetErr(err)
+		return cmd
+	}
+	cmd.val = size
+	return cmd
+}