[feature] support show collation

## Summary
support show collation, show charset  used by DBeaver.

```
mysql> show collation;
ERROR 1105 (HY000): unsupported.query:show collation
```

```
mysql> show charset;
ERROR 1149 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use, syntax error at position 13 near 'charset'
```