ddb: MySQL support

[yznts]

Provide initial mysql support

[yznts]

This might be challenging for multiple reasons:

• Certificate support requires additional effort and not handled by driver's DSN parser
• Go's mysql driver defaults to []uint8 on .Scan() to any type, so it doesn't actually resolve type

[yznts]

Just to ensure, I've added types output for dsql in this way:

for _, row := range data.Rows {
	for _, element := range row {
		fmt.Printf("%v  ", reflect.TypeOf(element))
	}
	fmt.Println()
}

Using sakiladb/mysql and sakiladb/postgres as example.
Sample query: select * from address limit 1

For postgres, we're getting types correctly:

$ go run ./cmd/dsql "select * from address limit 1"
int64  string  <nil>  string  int64  <nil>  string  time.Time
...

But, for mysql we're getting this:

$ go run ./cmd/dsql "select * from address limit 1"
int64  []uint8  <nil>  []uint8  int64  []uint8  []uint8  []uint8  []uint8
...

[yznts]

Related ticket: go-sql-driver/mysql#861

[yznts]

Closing for now, with future improvements intention