Add support for DEFAULT keyword for INSERT statement

[BoseSean]

Use case

create table table1
(
    field1 Int32,
    field2 Int32,
    field3 Int32 default CAST(1337, 'Int32'),
    field4 Int32 default CAST(1337, 'Int32')
)engine = MergeTree() PARTITION BY field1 
ORDER BY (field1, field2) 
SETTINGS index_granularity = 8192;

insert into table1 (field1, field3) values (5, DEFAULT)
insert into table1 values (5, DEFAULT, 10, DEFAULT)

Result:

field1	field2	field3	field4
5	0	1337	1337
5	0	10	1337

Additional context
With the DEFAULT keyword, insertion of data would have a bit more flexibility. And, let data with some missing values utilize bulk loading.

[filimonov]

Sounds reasonable, supported by most of popular DBMS (including MySQL, Postgres, MsSQL etc)

[tavplubix]

After #7215 NULL keyword can be used as DEFAULT if input_format_null_as_default=1 and column type is not Nullable

[alexey-milovidov]

It can be implemented quite easily.

[0over]

I would like to try this. @alexey-milovidov

[alexey-milovidov]

@1over Do you have any troubles implementing it? Do you need help?

[0over]

@alexey-milovidov no troubles yet, I was occupied with other things. I plan to finish it in the coming days