Only show cookie banner if consent required

We already have analytics code that doesn't depend on getting consent
from users and we don't want that to break. So the consent process will
be opt in via config, at least initially

Author: yndajas

lib/source/layouts/core.erb

@@ -52,29 +52,31 @@
     <script>document.body.className += ' js-enabled' + ('noModule' in HTMLScriptElement.prototype ? ' govuk-frontend-supported' : '');</script>
 
     <div class="app-pane">
-      <div class="govuk-cookie-banner" data-nosnippet role="region" aria-label="Cookies on <%= config[:tech_docs][:service_name] %>">
-        <div class="govuk-cookie-banner__message govuk-width-container">
-          <div class="govuk-grid-row">
-            <div class="govuk-grid-column-two-thirds">
-              <h2 class="govuk-cookie-banner__heading govuk-heading-m">
-                Cookies on <%= config[:tech_docs][:service_name] %>
-              </h2>
-              <div class="govuk-cookie-banner__content">
-                <p class="govuk-body">We’d like to use analytics cookies so we can understand how you use the service and make improvements.</p>
+      <% if config[:tech_docs][:ga4_gtm_tracking_id].is_a?(String) && !config[:tech_docs][:ga4_gtm_tracking_id].empty? %>
+        <div class="govuk-cookie-banner" data-nosnippet role="region" aria-label="Cookies on <%= config[:tech_docs][:service_name] %>">
+          <div class="govuk-cookie-banner__message govuk-width-container">
+            <div class="govuk-grid-row">
+              <div class="govuk-grid-column-two-thirds">
+                <h2 class="govuk-cookie-banner__heading govuk-heading-m">
+                  Cookies on <%= config[:tech_docs][:service_name] %>
+                </h2>
+                <div class="govuk-cookie-banner__content">
+                  <p class="govuk-body">We’d like to use analytics cookies so we can understand how you use the service and make improvements.</p>
+                </div>
               </div>
             </div>
-          </div>
-          <div class="govuk-button-group">
-            <button type="button" class="govuk-button" data-module="govuk-button">
-              Accept analytics cookies
-            </button>
-            <button type="button" class="govuk-button" data-module="govuk-button">
-              Reject analytics cookies
-            </button>
-            <a class="govuk-link" href="#">View cookies</a>
+            <div class="govuk-button-group">
+              <button type="button" class="govuk-button" data-module="govuk-button">
+                Accept analytics cookies
+              </button>
+              <button type="button" class="govuk-button" data-module="govuk-button">
+                Reject analytics cookies
+              </button>
+              <a class="govuk-link" href="#">View cookies</a>
+            </div>
           </div>
         </div>
-      </div>
+      <% end %>
       <div class="app-pane__header toc-open-disabled">
         <a href="#content" class="govuk-skip-link" data-module="govuk-skip-link">Skip to main content</a>