feat: Add S3 support

[pavelzw]

Description

xref #960

#960 (comment)

[pavelzw]

a current limitation is that we need to have one shared credential for each bucket we access with this setup.
we could also make the config-file and profile channel-dependent but i think as a first version, this is okay, wdyt?

[baszalmstra]

If you would add specific config per channel what would that look like? Does it change the API much?

[delsner]

we could also make the config-file and profile channel-dependent

I think this comment was based on an outdated version of the code. Still, we do not support channel-specific configuration yet. Did you already think about an API @pavelzw?

[pavelzw]

from the API side, i'm thinking of something like

#[derive(Clone, Debug)]
pub struct S3 {
    auth_storage: AuthenticationStorage,
    default_config: S3Config,
    // prefix -> config map, overrides default_config
    channel_config: HashMap<String, S3Config>,
    expiration: std::time::Duration,
}

In create_s3_client we would gather the config for the respective bucket or falling back to the default config.

It can be configured in pixi.toml (or global config respectively)

[s3-config]
endpoint-url = "https://s3.aws..."
region = "eu-central-1"
force-path-style = false

[channel."s3://my-bucket".s3-config]
endpoint-url = "https://localhost:9000"
region = "eu-west-1"
force-path-style = true

From a pixi.toml perspective, this should be backwards compatible so I think it's fine to not implement this yet but only if the need arises.