feat(query): Support generate virtual columns

[b41sh]

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Summary

Support generating virtual columns

Add the following SQLs to create, drop and generate virtual columns:

create virtual columns (<expr>, ..) for <table>
alter virtual columns (<expr>, ..) for <table>
drop virtual columns for <table>
generate virtual columns for <table>

Using a log analysis script to get which JSON internal fields are frequently queried and then calls create virtual columns .. to create virtual columns for these fields, and then calls generate virtual columns .. to generate virtual columns. Once the virtual columns have been generated, we can read the data from the JSON internal fields directly through the virtual columns.

for example:

create table test (id int, val json);
insert into test values(1, '{"a":33,"b":44}'),(2, '{"a":55,"b":66}');
create virtual columns (val['a'], val['b']) for test;
generate virtual columns for test;

select val['a'], val['b'] from test;
+----------+----------+
| val['a'] | val['b'] |
+----------+----------+
| 33       | 44       |
| 55       | 66       |
+----------+----------+

Part of #6994

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[RinChanNOWWW]

What does Using a log analysis script to get which JSON internal fields are frequently queried mean?

[b41sh]

What does Using a log analysis script to get which JSON internal fields are frequently queried mean?

We want the virtual columns to be generated automatically, without the user having to create them manually. So a Python script is needed to analyze the query log, find the internal JSON fields that are frequently queried, and call the add virtual columns and generate virtual columns commands to generate the virtual columns. This script can be implemented in the next PR.

[BohuTANG]

cc @soyeric128 for documentation, thanks.