feat: custom type implements autoIncrement

[ruanlang]

User Case Description

ID int64 gorm:"column:id;type:bigint(20) unsigned;primaryKey;autoIncrement:true" json:"id"
go-gorm/gorm#5505 @jinzhu @a631807682

[a631807682]

@ruanlang Sorry, I made a mistake.

1. We need to support gorm:"type:int(20) AUTO_INCREMENT" and gorm:"type:int;autoIncrement", so we still need to check if AUTO_INCREMENT already exists.
2. I'm not sure what the situation here needs to recheck TagSettings, can you give me an example?
3. When we check AUTOINCREMENT tag, we should check the value is true or false, refer to https://github.com/go-gorm/gorm/blob/master/schema/field.go#L113

[ruanlang]

We are used to using AUTO_INCREMENT in SQL statements, so check TagSettings["AUTO_INCREMENT"] @a631807682

[ruanlang]

@a631807682 Sorry, use autoIncrement by convention, specifies column auto incrementable

[a631807682]

@ruanlang as the first item of the last review said, you also need to check if AUTO_INCREMENT exists, otherwise there may be cases like this:
gorm:"type:int(20) AUTO_INCREMENT" -> type:int(20) AUTO_INCREMENT AUTO_INCREMENT
because the primary key AutoIncrement is true by default

if !strings.Contains(strings.ToLower(string(field.DataType)), " auto_increment")