Fix AutoMigrate default value comparison for string fields (issue #7590) (#7591)

* feat:Capitalize the priority field of IndexOption so that other systems can access this field from outside the package.

* bugfix:AutoMigrate https://github.com/go-gorm/gorm/issues/7590

* bugfix:defaultValue DefaultValue

* feat：change to strings.Trim(field.DefaultValue, "'\"") for alterColumn