Introduce SORTBY plan hint for insert statements

In order to improve compression and/or the effectiveness of min/max pruning, it is desirable to control the order in which rows are inserted into table (mostly for Parquet).

To that end, we should introduce a "sortby" plan hint for insert statements: Example

CREATE TABLE dst (...);
INSERT INTO dst /*+ sortby(day,hour) */ SELECT * FROM src;

This would produce the following plan:
SCAN -> SORT(day,hour) -> TABLE SINK

Syntax and behavior

 INSERT INTO dst /*+ sortby(day,hour) */ SELECT * FROM src; 

• We will not support the legacy-hint style with brackets

  [sortby(day,hour)]

• To keep the "clustered" hint strictly separate from the "sortby" hint, it is only legal to use non-partition columns in "sortby" for HDFS tables.
• Similarly, it is only legal to mention non-primary-key columns of Kudu tables.