FIX: Send new topic Slack notifications to the correct thread

This applies when topics are created using the slack transcript feature, and there is a rule configured with filter=thread

lib/discourse_chat/provider/slack/slack_provider.rb

@@ -112,6 +112,7 @@ def self.send_via_api(post, channel, message)
     if message.key?(:thread_ts)
       data[:thread_ts] = message[:thread_ts]
     elsif match = slack_thread_regex.match(post.raw)
+      data[:thread_ts] = match.captures[1]
       post.topic.slack_thread_id = match.captures[1]
       post.topic.save_custom_fields
     end

spec/lib/discourse_chat/provider/slack/slack_provider_spec.rb

@@ -120,15 +120,17 @@
       it 'recognizes slack thread ts in comment' do
         post.update!(cooked: "cooked", raw: <<~RAW
              My fingers are typing words that improve `raw_quality`
-             <!--SLACK_CHANNEL_ID=UIGNOREFORNOW;SLACK_TS=1501801629.052212-->
+             <!--SLACK_CHANNEL_ID=UIGNOREFORNOW;SLACK_TS=#{@ts}-->
         RAW
         )
 
         rule = DiscourseChat::Rule.create(channel: @channel, filter: "thread")
         post.topic.slack_thread_id = nil
 
         described_class.trigger_notification(post, chan1, rule)
-        expect(post.topic.slack_thread_id).to eq('1501801629.052212')
+        expect(post.topic.slack_thread_id).to eq(@ts)
+
+        expect(@thread_stub).to have_been_requested.times(1)
       end
 
       it 'handles errors correctly' do