feat: drop column for alter table

[killme2008]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Try to fix #466, which supports alter table drop column [name]:

mysql> create table test(host STRING, ts timestamp, time index(ts));
Query OK, 1 row affected (0.03 sec)

mysql> insert into test values('a', 1);
Query OK, 1 row affected (0.03 sec)

mysql> insert into test values('b', 2);
Query OK, 1 row affected (0.04 sec)

mysql> select * from test;
+------+---------------------+
| host | ts                  |
+------+---------------------+
| a    | 1970-01-01 00:00:00 |
| b    | 1970-01-01 00:00:00 |
+------+---------------------+
2 rows in set (0.01 sec)
mysql> alter table test drop column host;
Query OK, 0 rows affected (0.03 sec)

mysql> select * from test;
+---------------------+
| ts                  |
+---------------------+
| 1970-01-01 00:00:00 |
| 1970-01-01 00:00:00 |
+---------------------+
2 rows in set (0.01 sec)

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #562 (bb03581) into develop (8faa6b0) will decrease coverage by 0.03%.
The diff coverage is 67.79%.

@@             Coverage Diff             @@
##           develop     #562      +/-   ##
===========================================
- Coverage    86.38%   86.35%   -0.04%     
===========================================
  Files          398      398              
  Lines        50042    50165     +123     
===========================================
+ Hits         43229    43320      +91     
- Misses        6813     6845      +32     

Flag	Coverage Δ
rust	86.35% <67.79%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/datanode/src/server/grpc/ddl.rs	88.81% <0.00%> (-3.57%)	⬇️
src/sql/src/statements/alter.rs	31.57% <0.00%> (-3.72%)	⬇️
src/table/src/requests.rs	25.00% <ø> (ø)
src/sql/src/parsers/alter_parser.rs	87.83% <90.62%> (+4.11%)	⬆️
src/datanode/src/sql/alter.rs	90.90% <100.00%> (+0.36%)	⬆️
src/mito/src/engine.rs	97.35% <100.00%> (ø)
src/mito/src/table.rs	88.57% <100.00%> (ø)
src/table/src/metadata.rs	96.30% <100.00%> (ø)
src/servers/src/mysql/handler.rs	64.13% <0.00%> (-1.09%)	⬇️
src/frontend/src/table.rs	91.72% <0.00%> (-1.07%)	⬇️
... and 9 more

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[v0y4g3r]

LGTM