What this PR does / why we need it:

This PR introduces the ability to override the sts endpoint used to authenticate with the AWS sdk / thanos s3 provider. It also provides a path to use STS authentication with minio operator.

As a note for those who try the minio operator STS auth: the AWS SDK adds a trailing slash when calling STS endpoint, which will cause the auth call to fail with 404. An nginx proxy can fix this the following config:

    location /sts/platform/ {
      resolver kube-dns.kube-system.svc.cluster.local;

      # Forward the request to the upstream server
      proxy_pass https://<ACTUAL ADDRESS OF THE STS SERVICE FOR MINIO OPERATOR>;
      proxy_set_header Host $host;
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header X-Forwarded-Proto $scheme;

      # Preserve the original request method
      proxy_method $request_method;
    }

Which issue(s) this PR fixes:
Fixes #10751

Special notes for your reviewer:

Checklist

• Reviewed the [CONTRIBUTING.md]
  (https://github.com/grafana/loki/blob/main/CONTRIBUTING.md) guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
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