implement EXPLAIN and EXPLAIN PLAN

[jycor]

Moving our current implementation of EXPLAIN to EXPLAIN PLAN, and replace EXPLAIN with a dummy implementation of MySQL's EXPLAIN

Looks like this now:

tmp2/main> explain select * from t;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| 1  | SELECT      | NULL  | NULL       | NULL | NULL          | NULL | NULL    | NULL | NULL | NULL     |       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
1 row in set (0.00 sec)

tmp2/main> explain plan select * from t;
+------------------+
| plan             |
+------------------+
| Table            |
|  ├─ name: t      |
|  └─ columns: [i] |
+------------------+
3 rows in set (0.00 sec)

related: dolthub/dolt#8592

[max-hoffman]

lgtm, seems like it might be a bit disruptive

[max-hoffman]

do you wanna do this in this PR?

[jycor]

might as well

[jycor]

oh wait, this is from vitess having a newer version of go...

[max-hoffman]

maybe include a warning as long as the output isn't useful