Add `gitlab_rails['auto_migrate'] = false` to HA docs for Redis/PG [ci skip]

In a high availability configuration, the Redis and PostgreSQL nodes
should not attempt to run database migrations. In fact, trying will
result in errors about not providing a database password. To
prevent errors and confusion, add this configurtion to these nodes'
`gitlab.rb` file.

doc/administration/high_availability/database.md

@@ -44,6 +44,9 @@ If you use a cloud-managed service, or provide your own PostgreSQL:
     gitlab_rails['db_password'] = 'DB password'
     postgresql['md5_auth_cidr_addresses'] = ['0.0.0.0/0']
     postgresql['listen_address'] = '0.0.0.0'
+
+    # Disable automatic database migrations
+    gitlab_rails['auto_migrate'] = false
     ```
 
 1. Run `sudo gitlab-ctl reconfigure` to install and configure PostgreSQL.
@@ -102,9 +105,6 @@ If you use a cloud-managed service, or provide your own PostgreSQL:
 1. Exit the database prompt by typing `\q` and Enter.
 1. Exit the `gitlab-psql` user by running `exit` twice.
 1. Run `sudo gitlab-ctl reconfigure` a final time.
-1. Run `sudo touch /etc/gitlab/skip-auto-migrations` to prevent database migrations
-   from running on upgrade. Only the primary GitLab application server should
-   handle migrations.
 
 ---
 

doc/administration/high_availability/redis.md

@@ -287,14 +287,14 @@ The prerequisites for a HA Redis setup are the following:
     redis['password'] = 'redis-password-goes-here'
     ```
 
-1. To prevent database migrations from running on upgrade, run:
+1. Only the primary GitLab application server should handle migrations. To
+   prevent database migrations from running on upgrade, add the following
+   configuration to your `/etc/gitlab/gitlab.rb` file:
 
     ```
-    sudo touch /etc/gitlab/skip-auto-migrations
+    gitlab_rails['auto_migrate'] = false
     ```
 
-    Only the primary GitLab application server should handle migrations.
-
 1. [Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
 
 ### Step 2. Configuring the slave Redis instances