diff: add collation config

[WangXiangUSTC]

for example, we execute these sqls in mysql and tidb:

CREATE TABLE `test_collation` (  `name` varchar(24) DEFAULT NULL );
insert into test_collation values("A");
insert into test_collation values("D");
insert into test_collation values("C");
insert into test_collation values("b")

show create table in mysql:

mysql> show create table test_collation \G
*************************** 1. row ***************************
       Table: test_colltion
Create Table: CREATE TABLE `test_colltion` (
  `name` varchar(24) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

show create table in tidb:

mysql> show create table test_collation \G
*************************** 1. row ***************************
       Table: test_colltion
Create Table: CREATE TABLE `test_collation ` (
  `name` varchar(24) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin
1 row in set (0.01 sec)

then we select the max and min value:
in mysql:

mysql> select min(name), max(name) from test_collation;
+-----------+-----------+
| min(name) | max(name) |
+-----------+-----------+
| A         | D         |
+-----------+-----------+
1 row in set (0.00 sec)

in tidb:

mysql> select min(name), max(name) from test_collation;
+-----------+-----------+
| min(name) | max(name) |
+-----------+-----------+
| A         | b         |
+-----------+-----------+
1 row in set (0.01 sec)

we can see the max(name) is not equal, but we can use collation to let the result equal, execute this sql in mysql:

select min(name collate latin1_bin), max(name collate latin1_bin) from test_collation;
+------------------------------+------------------------------+
| min(name collate latin1_bin) | max(name collate latin1_bin) |
+------------------------------+------------------------------+
| A                            | b                            |
+------------------------------+------------------------------+
1 row in set (0.00 sec)

[IANTHEREAL]

update example

[IANTHEREAL]

is info better?

[IANTHEREAL]

Rest LGTM

[IANTHEREAL]

@csuzhangxc PTAL

[IANTHEREAL]

LGTM