new feature: allow to set proxy for s3 service

[trim21]

Feature Description

I'm using python binding and it would be nice to allow to set proxy per operator without change the global env

Problem and Solution

I'm using s3 between GFW which would need some proxy to get good connection quality , but it's not possible to set proxy for just one operator.

It would be nice to allow set a proxy for a operator:

opendal.Operator(
    "s3",
    ...,
    proxy="...",
)

Additional Context

No response

Are you willing to contribute to the development of this feature?

• [ ] Yes, I am willing to contribute to the development of this feature.

[Xuanwo]

I think it's a general problem: how do we expose config from core to bindings? Rust user can just use its own HTTP client, but we need to pick one for Python.

My current idea is that we can have a general config system so users can set the behavior details for every component in the core.