feat: derive default credentials from aws sdk

[baszalmstra]

This PR adds support for getting S3 credentials directly from the AWS SDK. This adds support for using all the different ways you can sign in with AWS, e.g. keys, IAM Identity Center workforce, etc.

The goal of this PR is to enable only stating an s3 url (e.g. s3://my-awesome-channel) and let rattler figure out how to authenticate. The order of getting credentials is, 1) from the CLI (or environment variables), 2) from the default rattler authentication provider, 3) from the AWS SDK. This PR effectively adds option 3.

1. rattler_networking already supported this behavior but I found a few cases where error messages where very unclear. Especially around using invalid regions. I improved the error messages.
2. rattler_index required making some CLI arguments optional and using the AWS SDK to derive these values. When the system is properly configured rattler-index s3 s3://my-awesome-channel should "just work".
3. rattler_upload required making the same changes. I also added a few preconditions to not upload shards if they already exist, and I added some other small changes. The goal is that rattler upload s3 --channel s3://my-awesome-channel <packages> should just work.

I still want to add an e2e test where we set up a minio instance, upload a package, index the channel and create an environment from the channel without any additional configuration.

Duplicate of #1627, created this one to allow creating a PR on this repository to allow for OIDC to work.

[pavelzw]

thanks for the work! some comments

[pavelzw]

while you're at it, what about adding cloudflare r2 integration tests as well in this file? @delsner and i definitely wrote some at some point, not sure whether in this repo or in pixi/rattler-build only.

[delsner]

I think it was in this repo:

rattler/crates/rattler_networking/tests/s3_integration_test.rs

Lines 18 to 39 in b3eff34

	#[fixture]
	fn r2_host() -> String {
	"https://e1a7cde76f1780ec06bac859036dbaf7.eu.r2.cloudflarestorage.com".into()
	}
	#[fixture]
	fn r2_credentials() -> Option<(String, String)> {
	let r2_access_key_id = std::env::var("RATTLER_TEST_R2_READONLY_ACCESS_KEY_ID").ok();
	let r2_secret_access_key = std::env::var("RATTLER_TEST_R2_READONLY_SECRET_ACCESS_KEY").ok();
	if r2_access_key_id.is_none()
	|| r2_access_key_id.clone().unwrap().is_empty()
	|| r2_secret_access_key.is_none()
	|| r2_secret_access_key.clone().unwrap().is_empty()
	{
	eprintln!(
	"Skipping test as RATTLER_TEST_R2_READONLY_ACCESS_KEY_ID or RATTLER_TEST_R2_READONLY_SECRET_ACCESS_KEY is not set"
	);
	None
	} else {
	Some((r2_access_key_id.unwrap(), r2_secret_access_key.unwrap()))
	}
	}