chore: Slack file upload changes (#10903)

The Slack `files.upload` API endpoint is deprecated and will stop
functioning on March 11, 2025. In this PR, we have implemented the
changes for the [new file
upload](https://api.slack.com/messaging/files#uploading_files) method.

lib/integrations/slack/send_on_slack_service.rb

@@ -119,12 +119,14 @@ class Integrations::Slack::SendOnSlackService < Base::SendOnChannelService
   def upload_file
     return unless message.attachments.first.with_attached_file?
 
-    result = slack_client.files_upload({
-      channels: hook.reference_id,
+    result = slack_client.files_upload_v2(
+      filename: message.attachments.first.file.filename,
+      content: message.attachments.first.file.download,
       initial_comment: 'Attached File!',
-      thread_ts: conversation.identifier
-    }.merge(file_information))
-    Rails.logger.info(result)
+      thread_ts: conversation.identifier,
+      channel_id: hook.reference_id
+    )
+    Rails.logger.info "slack_upload_result: #{result}"
   end
 
   def file_type