Add a Lettuce-based Redis singleton client.

service/src/main/java/org/whispersystems/textsecuregcm/configuration/RedisConfiguration.java

@@ -23,6 +23,7 @@ import org.hibernate.validator.constraints.URL;
 
 import javax.validation.Valid;
 import javax.validation.constraints.NotNull;
+import java.time.Duration;
 import java.util.List;
 
 public class RedisConfiguration {
@@ -35,6 +36,10 @@ public class RedisConfiguration {
   @NotNull
   private List<String> replicaUrls;
 
+  @JsonProperty
+  @NotNull
+  private Duration timeout = Duration.ofSeconds(10);
+
   @JsonProperty
   @NotNull
   @Valid
@@ -48,6 +53,10 @@ public class RedisConfiguration {
     return replicaUrls;
   }
 
+  public Duration getTimeout() {
+    return timeout;
+  }
+
   public CircuitBreakerConfiguration getCircuitBreakerConfiguration() {
     return circuitBreaker;
   }