New function to gather users tables data information

[ethervoid]

                                                          QUERY PLAN                                                          
------------------------------------------------------------------------------------------------------------------------------
 Function Scan on cdb_usertablesdata  (cost=0.25..10.25 rows=1000 width=112) (actual time=621.533..621.704 rows=1505 loops=1)
 Planning time: 0.045 ms
 Execution time: 621.848 ms
(3 rows)

explain analyze select * from cdb_userdatasize('hugeuser');
                                                     QUERY PLAN                                                      
---------------------------------------------------------------------------------------------------------------------
 Function Scan on cdb_userdatasize  (cost=0.25..0.26 rows=1 width=8) (actual time=2037.431..2037.431 rows=1 loops=1)
 Planning time: 0.039 ms
 Execution time: 2037.458 ms
(3 rows)```

[Algunenano]

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