FIX: Use dualstack S3 endpoint for direct uploads (#29611)

When we added direct S3 uploads to Discourse, which use
presigned URLs, we never took into account the dualstack
endpoints for IPv6 on S3.

This commit fixes the issue by using the dualstack endpoints
for presigned URLs and requests, which are used in the
get-presigned-put and batch-presign-urls endpoints used when
directly uploading to S3.

It also makes regular S3 requests for `put` and so on use
dualstack URLs. It doesn't seem like there is a downside to
doing this, but a bunch of specs needed to be updated to reflect this.

lib/s3_helper.rb

@@ -50,6 +50,7 @@ class S3Helper
     options[:client] = s3_client if s3_client.present?
     options[:use_accelerate_endpoint] = !for_backup &&
       SiteSetting.Upload.enable_s3_transfer_acceleration
+    options[:use_dualstack_endpoint] = SiteSetting.Upload.use_dualstack_endpoint
 
     bucket =
       if for_backup
@@ -265,6 +266,7 @@ class S3Helper
 
     opts[:endpoint] = SiteSetting.s3_endpoint if SiteSetting.s3_endpoint.present?
     opts[:http_continue_timeout] = SiteSetting.s3_http_continue_timeout
+    opts[:use_dualstack_endpoint] = SiteSetting.Upload.use_dualstack_endpoint
 
     unless obj.s3_use_iam_profile
       opts[:access_key_id] = obj.s3_access_key_id
@@ -362,6 +364,7 @@ class S3Helper
         key: key,
         expires_in: expires_in,
         use_accelerate_endpoint: @s3_options[:use_accelerate_endpoint],
+        use_dualstack_endpoint: @s3_options[:use_dualstack_endpoint],
       }.merge(opts),
     )
   end
@@ -380,6 +383,7 @@ class S3Helper
         key: key,
         expires_in: expires_in,
         use_accelerate_endpoint: @s3_options[:use_accelerate_endpoint],
+        use_dualstack_endpoint: @s3_options[:use_dualstack_endpoint],
       }.merge(opts),
     )
   end