OGM-1474 Replace CREATE UNIQUE in Cypher queries with MERGE

  Running CREATE UNIQUE queries will generate the following warning:

  ```
  The RULE planner is not available in the current CYPHER version,
  the query has been run by an older CYPHER version. CREATE UNIQUE is unsupported
  for current CYPHER version, the query has been execute by an older CYPHER version
  ```

neo4j/src/main/java/org/hibernate/ogm/datastore/neo4j/dialect/impl/BaseNeo4jAssociationQueries.java

@@ -104,7 +104,7 @@ private static String initFindRelationshipQuery(EntityKeyMetadata ownerEntityKey
 
 	/*
 	 * MATCH (o:ENTITY:table1 {id: {0}}), (t:ENTITY:table2 {id: {1}})
-	 * CREATE UNIQUE (o) -[r:role {props}]-> (t)
+	 * MERGE (o) -[r:role {props}]-> (t)
 	 * RETURN r
 	 */
 	private static String initCreateRelationshipQuery(EntityKeyMetadata ownerEntityKeyMetadata, AssociationKeyMetadata associationKeyMetadata) {
@@ -115,7 +115,7 @@ private static String initCreateRelationshipQuery(EntityKeyMetadata ownerEntityK
 		queryBuilder.append( ", " );
 		offset += ownerEntityKeyMetadata.getColumnNames().length;
 		appendEntityNode( "t", targetEntityKeyMetadata, queryBuilder, offset );
-		queryBuilder.append( " CREATE UNIQUE (n)" );
+		queryBuilder.append( " MERGE (n)" );
 		queryBuilder.append( " -[r" );
 		queryBuilder.append( ":" );
 		appendRelationshipType( queryBuilder, associationKeyMetadata );
@@ -347,7 +347,7 @@ private boolean isCollectionOfPrimitives(String collectionRole, String[] embedde
 	 * Example 1:
 	 *
 	 * MATCH (owner:ENTITY:MultiAddressAccount {login: {0}})
-	 * CREATE UNIQUE (owner) -[r:addresses {name: {1}}]-> (target:EMBEDDED:`MultiAddressAccount_addresses` {city: {2}, country: {3}})
+	 * MERGE (owner) -[r:addresses {name: {1}}]-> (target:EMBEDDED:`MultiAddressAccount_addresses` {city: {2}, country: {3}})
 	 * RETURN r
 	 *
 	 * Example 2:
@@ -360,11 +360,11 @@ private void createRelationshipforCollectionOfComponents(AssociationKey associat
 		int offset = associationKey.getEntityKey().getColumnNames().length;
 		if ( isPartOfEmbedded( collectionRole ) ) {
 			String[] pathToEmbedded = appendEmbeddedNodes( collectionRole, queryBuilder );
-			queryBuilder.append( " CREATE UNIQUE (e) -[r:" );
+			queryBuilder.append( " MERGE (e) -[r:" );
 			appendRelationshipType( queryBuilder, pathToEmbedded[pathToEmbedded.length - 1] );
 		}
 		else {
-			queryBuilder.append( " CREATE UNIQUE (owner) -[r:" );
+			queryBuilder.append( " MERGE (owner) -[r:" );
 			appendRelationshipType( queryBuilder, collectionRole );
 		}
 		appendProperties( queryBuilder, associationKey.getMetadata().getRowKeyIndexColumnNames(), offset );