Create the gitlabhq_production DB manually

What does this MR do?

When setting up an external DB with GitLab, GitLab doesn't actually create the gitlabhq_production database. If the user attempts to follow our current instructions and performs a sudo gitlab-ctl reconfigure, they will see this error:

There was an error running gitlab-ctl reconfigure:

bash[migrate gitlab-rails database] (gitlab::database_migrations line 55) had an error: Mixlib::ShellOut::ShellCommandFailed: Expected process to exit with [0], but received '1'
---- Begin output of "bash"  "/tmp/chef-script20200827-3947-eanl7b" ----
STDOUT: rake aborted!
ActiveRecord::NoDatabaseError: FATAL:  database "gitlabhq_production" does not exist
/opt/gitlab/embedded/service/gitlab-rails/lib/tasks/gitlab/db.rake:48:in `block (3 levels) in <top (required)>'
/opt/gitlab/embedded/bin/bundle:23:in `load'
/opt/gitlab/embedded/bin/bundle:23:in `<main>'

Caused by:
PG::ConnectionBad: FATAL:  database "gitlabhq_production" does not exist
/opt/gitlab/embedded/service/gitlab-rails/lib/tasks/gitlab/db.rake:48:in `block (3 levels) in <top (required)>'
/opt/gitlab/embedded/bin/bundle:23:in `load'
/opt/gitlab/embedded/bin/bundle:23:in `<main>'
Tasks: TOP => gitlab:db:configure
(See full trace by running task with --trace)
STDERR:
---- End output of "bash"  "/tmp/chef-script20200827-3947-eanl7b" ----
Ran "bash"  "/tmp/chef-script20200827-3947-eanl7b" returned 1

Therefore, it's necessary for the user to create the gitlabhq_production database manually.

cc @atanayno

Related issues

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