copr-dist-git: add custom httpd message for disabled cgit

Fix https://github.com/fedora-copr/copr/issues/3595

roles/copr/dist_git/files/cgit-error.html

@@ -0,0 +1,9 @@
+<h1>The cgit interface is temporarily unavailable</h1>
+<p>
+  We had to temporarily disable the cgit interface for Copr DistGit because it
+  was causing performance issues. Copr builders clone the repositories from a
+  different URL (and you can do too) so building packages is unaffected.
+</p>
+<p>
+  Ticket: <a href="https://github.com/fedora-copr/copr/issues/3591">#3591</a>
+</p>

roles/copr/dist_git/files/httpd/copr-dist-git.conf

@@ -12,3 +12,7 @@ Alias /per-task-logs /var/lib/copr-dist-git/per-task-logs
     ServerLimit          20
     MaxRequestsPerChild   10000
 </IfModule>
+
+# When disabling cgit with the `chmod -x /var/www/cgi-bin/cgit` hack,
+# please uncomment this line
+ErrorDocument 500 /cgit-error.html

roles/copr/dist_git/tasks/main.yml

@@ -102,6 +102,11 @@
   tags:
   - config
 
+- name: Install cgit error message
+  ansible.builtin.copy: src="cgit-error.html" dest="/var/www/html/" mode=0644
+  tags:
+  - config
+
 - name: Set up tmpwatch cron job
   cron: name="clean tmp" minute="0" job="/usr/sbin/tmpwatch 2h /tmp/"