Add caption and update duplicate log IDs in the banner

app/controllers/delete_logs_controller.rb

@@ -201,6 +201,6 @@ private
   end
 
   def duplicate_log_ids(logs)
-    logs.map { |log| "Log #{log.id}" }.join(", ")
+    logs.map { |log| "Log #{log.id}" }.to_sentence(last_word_connector: ' and ')
   end
 end

app/views/logs/delete_duplicates.html.erb

@@ -5,6 +5,7 @@
 
 <div class="govuk-grid-row">
   <div class="govuk-grid-column-two-thirds-from-desktop">
+    <span class="govuk-caption-l">Delete duplicate logs</span>
     <h1 class="govuk-heading-l">
       <%= content_for(:title) %>
     </h1>