Base implemment of default value for columns

[ygf11]

Describe This Problem

Support default value for columns in Ceresdb.

Proposal

Make default value work in some base sql statements. sqls:

• Create table.
• Insert table.
• Show create table.

For the default value option, now only support exprs which does not reference other columns, like 10, 1+1, now()..

Additional Context

#210