generic file permission handle

[jiefenghuang]

What would you like to be added: Generic file permission management module or handler

Since file permission checks require reading data from the meta engine's transactions, it may be necessary to encapsulate them into handlers.

Why is this needed:

now that all meta engine need to do the same permission logic

• related code is scattered and difficult to maintain and review.
• adding a new meta engine is also challenging.

https://github.com/juicedata/juicefs/blob/7b85645cac16c8442b3b7d35365a99dc0e339cdd/pkg/meta/redis.go#L1682-L1684

[jiefenghuang]

Perhaps all the APIs of the meta interface could be implemented as a generic workflow process, with meta.Engine abstracted as the data handle and transaction interface.