Adds missing step for adding shard to gitlab.rb in base role
Per this thread in slack, we are missing a step in the process to add a new Gitaly shard, meaning the newest two shards added in #6647 (closed) were not added to default['omnibus-gitlab']['gitlab_rb']['git_data_dirs']
hash in the gprd-base
chef role, and thus were not fully configured for all operations initiated from the rails console.
The chef role has been corrected in https://gitlab.com/gitlab-com/gl-infra/chef-repo/-/merge_requests/1720; This MR fixes the issue template for future changes.