feat: add SyncSchema as alias for AutoMigrate()

[ei-sugimoto]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

This PR is based on issue #7048.
GORM users will be able to perform automatic migration of database schemas using either AutoMigrate or SyncSchema.

User Case Description

gorm.AutoMigrate(&model.User{})
gorm.AutoMigrate(&model.Character{})
gorm.AutoMigrate(&model.UserCharacter{})

//or
gorm.SyncSchema(&model.User{})
gorm.SyncSchema(&model.Character{})
gorm.SyncSchema(&model.UserCharacter{})

[jinzhu]

Let's work together to improve the documentation. More APIs are not necessarily better for the project's development and can be ambiguous.