services/redis: Implement Write::append with native support

[Xuanwo]

All kv servcices are handling Write::append in memory:

https://github.com/datafuselabs/opendal/blob/88e3b0b3cd9bde47471b10c81bbec76ca286011a/src/raw/adapters/kv/backend.rs#L284-L288

But services like redis have native append support, for example: https://redis.io/commands/append/. We can adopt this feature to have a better append implement.

To support this, we need:

• Add append/blocking_append in kv adapter
• Use append if the kv backend has append support
• Implement append for redis service

[uran0sH]

I would like to work on it. Could you provide more details?

[Xuanwo]

Hi, @uran0sH, thank you for your interest! I have now updated the issue's description. Please take a look.

[uran0sH]

Ok, thank you. I will try to work on it.