feat: entity direct query supports specifying different spaces.

[CorvusYe]

as title:
zh: 为数据对象直接查询的功能，提供在实体注解中指定不同space的支持：

// Both are acceptable. The priority is: Space > Table
// 两种都行，优先级：Space > Table
@Space("test") 
@Table(name = "player", schema="test")
public class Player extends GraphBaseVertex {
  // ...
}

@Space("${nebula.space}") // from yml or configuration center
@Table(name = "player", schema="${nebula.space}")
public class Player extends GraphBaseVertex {
  // ...
}