[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/go.mod b/go.mod
index 472853d..e20e630 100644
--- a/go.mod
+++ b/go.mod
@@ -22,6 +22,7 @@
 	github.com/dgrijalva/jwt-go v3.2.0+incompatible // indirect
 	github.com/dustin/go-humanize v1.0.0 // indirect
 	github.com/eapache/go-resiliency v1.2.0
+	github.com/go-redis/redis/v8 v8.3.4
 	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
 	github.com/golang/protobuf v1.5.2
 	github.com/google/btree v1.0.1 // indirect