Make DynamoDBConfiguration more consistent.

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

@@ -8,42 +8,36 @@ package org.whispersystems.textsecuregcm.configuration;
 import com.fasterxml.jackson.annotation.JsonProperty;
 
 import javax.validation.Valid;
-import javax.validation.constraints.NotBlank;
 import javax.validation.constraints.NotEmpty;
 import java.time.Duration;
 
 public class DynamoDbConfiguration {
 
-    @JsonProperty
-    @NotBlank
     private String   region;
-
-    @JsonProperty
-    @NotBlank
     private String   tableName;
-
-    @JsonProperty
     private Duration clientExecutionTimeout = Duration.ofSeconds(30);
-
-    @JsonProperty
     private Duration clientRequestTimeout   = Duration.ofSeconds(10);
 
     @Valid
     @NotEmpty
+    @JsonProperty
     public String getRegion() {
         return region;
     }
 
     @Valid
     @NotEmpty
+    @JsonProperty
     public String getTableName() {
         return tableName;
     }
 
+    @JsonProperty
     public Duration getClientExecutionTimeout() {
         return clientExecutionTimeout;
     }
 
+    @JsonProperty
     public Duration getClientRequestTimeout() {
         return clientRequestTimeout;
     }