Add user's last used IP addresses to admin page

This would help admins figure out from where spam is originating.

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.4.0 (unreleased)
   - Bump fog to 1.36.0 (Stan Hu)
+  - Add user's last used IP addresses to admin page (Stan Hu)
   - Add housekeeping function to project settings page
   - The default GitLab logo now acts as a loading indicator
   - Fix caching issue where build status was not updating in project dashboard (Stan Hu)

app/views/admin/users/show.html.haml

@@ -70,6 +70,14 @@
             %strong.cred
               No
+        %li
+          %span.light Current sign-in IP:
+          %strong
+            - if @user.current_sign_in_ip
+              = @user.current_sign_in_ip
+            - else
+              never
+
         %li
           %span.light Current sign-in at:
           %strong
@@ -78,6 +86,14 @@
             - else
               never
+        %li
+          %span.light Last sign-in IP:
+          %strong
+            - if @user.last_sign_in_ip
+              = @user.last_sign_in_ip
+            - else
+              never
+
         %li
           %span.light Last sign-in at:
           %strong