how to use policy trigger by age, and the log append with {date}

i want to use log rolling by date, record 7days, is there any instructions?

expected 
```
rust_file:
    kind: rolling_file
    path: "logs/rust/{date}.log"
    encoder:
      pattern: "{d(%Y-%m-%d %H:%M:%S)} [{l}] {m}{n}"
    policy:
      compound:
        trigger:
          # 按天滚动
          age: 1d
        roller:
          # 保留最近7天的日志
          delete: {}
```
