feature: To support show next table id

[RingsC]

Is your feature request related to a problem? Please describe.

To show the next table id: which will get the next table id from tianmu.tid file.

To support these two statement.

select tianmu_next_table_id(); 
show @@tianmu_next_table_id;

Describe the solution you'd like

Describe alternatives you've considered

Additional context