fix(a11y): add titles to iframes

Author: machikoyasuda

pems_web/src/pems_web/districts/templates/districts/district.html

@@ -12,7 +12,9 @@ <h2>Form</h2>
     </div>
     <div class="row" style="min-height: 450px;">
         <div class="col-lg-12 border">
-            <iframe class="w-100 h-100" src="{{ streamlit.url }}/stations--stations?embed=true&district_number={{ current_district.number }}">
+            <iframe title="District {{ current_district.number }} visualization"
+                    class="w-100 h-100"
+                    src="{{ streamlit.url }}/stations--stations?embed=true&district_number={{ current_district.number }}">
             </iframe>
         </div>
     </div>

pems_web/src/pems_web/districts/templates/districts/index.html

@@ -24,7 +24,7 @@ <h2>Chart</h2>
                     </div>
                     <div class="row" style="min-height: 450px;">
                         <div class="col-lg-12 border">
-                            <iframe class="w-100 h-100" src="{{ streamlit.url }}/stations--stations?embed=true">
+                            <iframe title="District visualizations" class="w-100 h-100" src="{{ streamlit.url }}/stations--stations?embed=true">
                             </iframe>
                         </div>
                     </div>