Support INSERT INTO specific columns

Currently Flink only supports insert into a table without specifying columns, but most database systems support insert into specific columns by

INSERT INTO table_name(column1, column2, ...) ...

The columns not specified will be filled with default values or NULL if no default value is given when creating the table.

As Flink currently does not support default values when creating tables, we can fill the unspecified columns with NULL and throw exceptions if there are columns with NOT NULL constraints.