Added feature flag to show terraform banner

The aim of the flag is to add possibility to disable it for self-hosted
The feature flag is enabled by default

Changelog: added

app/helpers/projects_helper.rb

@@ -351,7 +351,7 @@ module ProjectsHelper
   end
 
   def show_terraform_banner?(project)
-    project.repository_languages.with_programming_language('HCL').exists? && project.terraform_states.empty?
+    Feature.enabled?(:show_terraform_banner, type: :ops, default_enabled: true) && project.repository_languages.with_programming_language('HCL').exists? && project.terraform_states.empty?
   end
 
   def project_permissions_panel_data(project)

config/feature_flags/ops/show_terraform_banner.yml

+---
+name: show_terraform_banner
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/71462
+rollout_issue_url: 
+milestone: '14.4'
+type: ops
+group: group::configure
+default_enabled: true

spec/helpers/projects_helper_spec.rb

@@ -904,6 +904,14 @@ RSpec.describe ProjectsHelper do
 
         it { is_expected.to be_falsey }
       end
+
+      context 'the :show_terraform_banner feature flag is disabled' do
+        before do
+          stub_feature_flags(show_terraform_banner: false)
+        end
+
+        it { is_expected.to be_falsey }
+      end
     end
   end