feat: Simplify SQL syntax that specifies timestamp key column

[dust1]

Which issue does this PR close?

Closes #115
ref #154

Rationale for this change

What changes are included in this PR?

I added 3 structs just to transmit the is_timestamp tag.
in ast.rs

Are there any user-facing changes?

now, user can use this sql to create table.

CREATE TABLE demo (
    name string TAG,
    value double NOT NULL,
    t timestamp NOT NULL TIMESTAMP KEY
) ENGINE=Analytic;

How does this change test

note

[waynexia]

We now have integration test suite for this kind of changes. Would you like to add this new syntax to it? Maybe some new SQLs in https://github.com/CeresDB/ceresdb/blob/main/tests/cases/local/05_ddl/create_tables.sql 🤗

[dust1]

We now have integration test suite for this kind of changes. Would you like to add this new syntax to it? Maybe some new SQLs in https://github.com/CeresDB/ceresdb/blob/main/tests/cases/local/05_ddl/create_tables.sql 🤗

sure! not adding test cases is my mistake😂

[waynexia]

We now have integration test suite for this kind of changes. Would you like to add this new syntax to it? Maybe some new SQLs in https://github.com/CeresDB/ceresdb/blob/main/tests/cases/local/05_ddl/create_tables.sql 🤗

sure! not adding test cases is my mistake😂

Not your fault! This is newly added. I'll add it to our dev guide

[ShiKaiWi]

@dust1 Thanks. It looks much better but I guess it can be made more simple.

[ShiKaiWi]

@dust1 Now it looks clean and pretty. And now maybe we should pay some attention to user's wrong use case.

[ShiKaiWi]

Thanks！