[BUG] URL scheme is ignored when sign_aws_requests is enabled

[riconnon]

What is the bug?

When sign_aws_requests is set the scheme from the url parameter is ignored and it always attempts to connect via HTTPS

How can one reproduce the bug?

1. Set URL to http://127.0.0.1:8080 or similar
2. Set sign_aws_requests to true
3. Make some requests

What is the expected behavior?

The requests are made via HTTP to the local address with AWS signature in the Authorization header

What is your host/environment?

macOS 15.1.1

Do you have any screenshots?

N/A

Do you have any additional context?

I'm using quite a peculiar setup which warrants this configuration.

I have a reverse proxy in front of my OpenSearch domain which listens for mTLS connections and forwards the requests to AWS OpenSearch.
For this I need to do AWS signing on my requests but also wrap that with mTLS to our custom endpoint.
Since our client certificates are typically stored in macOS keychain we can't configure this using client_cert_path and client_key_path so I was going to use a separate local signing proxy to do the signing which I have bound to a HTTP listener on a loopback address.

[bshien]

[Triage] Can you confirm if everything is ok with reverse proxy? See: #215 (comment) @rblcoder