Stop regenerating gitlab-pages-secret after each update

Previously gdk reconfigure would regenerate gitlab-pages-secret each time because the random string would differ each time. This happened because make touch-examples would touch every template (*.erb), causing all config files to be generated. We now exclude the gitlab-pages-secret.erb from this.

Closes #1438 (closed)

Testing

Have gitlab_pages.enabled in gdk.yml. For example:

gitlab_pages:
  host: pages.gdk.test
  enabled: true

Before

$ make touch-examples && make gitlab-pages-secret

ℹ️  'gitlab-pages-secret' has incoming changes:
-------------------------------------------------------------------------------------------------------------
@@ -1 +1 @@
-4BKKlshY6vHT1cyxUbbSVk6DxAU4iX+Ff03E4mB8RPY=
+KwoapBbV/olez2j2F8O5JLZqMb+LIWFGs41y1OLPvAc=

-------------------------------------------------------------------------------------------------------------
⚠️  WARNING: 'gitlab-pages-secret' has been overwritten. To recover the previous version, run:

cp -f '/Users/stanhu/gdk-ee/.backups/gitlab-pages-secret.20220512090357' \
'/Users/stanhu/gdk-ee/gitlab-pages-secret'

If you want to protect this file from being overwritten, see:
https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/configuration.md#overwriting-configuration-files
-------------------------------------------------------------------------------------------------------------

After

$ make touch-examples && make gitlab-pages-secret
$