[LocalProfileCreation]: Add divider line on the select avatar dialog

Fixed: 1162443
Change-Id: I32b86c1d8bb600e45920aaf508a2ad313354e930
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2645124Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Monica Basta <msalama@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846267}

chrome/browser/resources/signin/profile_picker/profile_creation_flow/local_profile_customization.html

@@ -227,7 +227,7 @@
       </cr-profile-avatar-selector>
     </div>
   </div>
-  <div id="buttonContainer" slot="button-container">
+  <div id="buttonContainer" slot="footer">
     <cr-button id="doneButton" class="action-button"
         on-click="onDoneSelectAvatarClick_">
       $i18n{selectAvatarDoneButtonLabel}