Remove Slack attachment in new issue presenter

https://gitlab.com/gitlab-org/gitlab/-/issues/324600

changelogs/unreleased/324600-new-issue-remove-attachment.yml

+---
+title: Remove Slack attachment from new issues created via Slash commands
+merge_request: 57431
+author:
+type: changed

lib/gitlab/slash_commands/presenters/issue_new.rb

@@ -12,16 +12,18 @@ module Gitlab
 
         private
 
-        def fallback_message
-          "New issue #{issue.to_reference}: #{issue.title}"
+        def pretext
+          "I created an issue on #{author_profile_link}'s behalf: *#{issue_link}* in #{project_link}"
         end
 
-        def fields_with_markdown
-          %i(title pretext text fields)
+        def issue_link
+          "[#{issue.to_reference}](#{project_issue_url(issue.project, issue)})"
         end
 
-        def pretext
-          "I created an issue on #{author_profile_link}'s behalf: *#{issue.to_reference}* in #{project_link}"
+        def response_message(custom_pretext: pretext)
+          {
+            text: pretext
+          }
         end
       end
     end

spec/lib/gitlab/slash_commands/presenters/issue_new_spec.rb

 # frozen_string_literal: true
-
 require 'spec_helper'
 
 RSpec.describe Gitlab::SlashCommands::Presenters::IssueNew do
+  include Gitlab::Routing
   let(:project) { create(:project) }
   let(:issue) { create(:issue, project: project) }
-  let(:attachment) { subject[:attachments].first }
 
   subject { described_class.new(issue).present }
 
   it { is_expected.to be_a(Hash) }
 
   it 'shows the issue' do
-    expect(subject[:response_type]).to be(:in_channel)
-    expect(subject).to have_key(:attachments)
-    expect(attachment[:title]).to start_with(issue.title)
+    expected_text = "I created an issue on <#{url_for(issue.author)}|#{issue.author.to_reference}>'s behalf: *<#{project_issue_url(issue.project, issue)}|#{issue.to_reference}>* in <#{project.web_url}|#{project.full_name}>"
+
+    expect(subject).to eq(
+      response_type: :in_channel,
+      status: 200,
+      text: expected_text
+    )
   end
 end