add string int and index limits for dynamodb

src/Database/Adapter/DynamoDB.php

@@ -673,22 +673,26 @@ public function getSizeOfCollection(string $collection): int
 
  /**
  * Get max STRING limit
+ * 
+ * DynamoDb string limits are governed by item size limit at 400 Kb - using MariaDB Limit for now.
  *
  * @return int
  */
  public function getLimitForString(): int
  {
- return 0;
+ return 4294967295;
  }
 
  /**
  * Get max INT limit
+ * 
+ * The actual limit is 9.9999999999999999999999999999999999999E+125 but the PHP Limit is obviously much less.
  *
  * @return int
  */
  public function getLimitForInt(): int
  {
- return 0;
+ return PHP_INT_MAX;
  }
 
  /**
@@ -705,11 +709,12 @@ public function getLimitForAttributes(): int
  /**
  * Get maximum index limit.
  *
+ * DynamoDb limit for Global Secondary Indexes.
  * @return int
  */
  public function getLimitForIndexes(): int
  {
- return 0;
+ return 20;
  }
 
  /**