Add CINE option for CREATE TABLE AS and CREATE MATERIALIZED VIEW

Fabrízio de Royes Mello reviewed by Rushabh Lathia.

src/include/nodes/parsenodes.h

@@ -2652,6 +2652,7 @@ typedef struct CreateTableAsStmt
 	IntoClause *into;			/* destination table */
 	ObjectType	relkind;		/* OBJECT_TABLE or OBJECT_MATVIEW */
 	bool		is_select_into; /* it was written as SELECT INTO */
+	bool		if_not_exists;	/* just do nothing if it already exists? */
 } CreateTableAsStmt;
 
 /* ----------------------