Clarified changed requirement for slash at end of gitlab_url. See https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5249#note_326997724

Since https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/181,
gitlab-shell no longer can talk to Redis directly. All operations
go through the internal API.

Removing this config is useful for several reasons:

1. It removes dead code.
2. Since the gitlab-shell config is repeatedly parsed with every git
action, removing a few lines can improve performance.
3. There is a bug in string handling when there are YAML characters
included in the Redis password field.

* Using custom_hooks_dir, not custom_hook_dir
* Fixed missed reference in gitlab.rb.template
* Using %r for regex's in specs that reference a path

* By default, do not populate this value
* Change value name to be config_hook_dir

Defaults to package provided directory, but allow the users to point to
their own location. Only updates the config.yml file for gitlab-shell,
assumes the user will manage the directory themselves.

* Using custom_hooks_dir, not custom_hook_dir
* Fixed missed reference in gitlab.rb.template
* Using %r for regex's in specs that reference a path

* By default, do not populate this value
* Change value name to be config_hook_dir

Defaults to package provided directory, but allow the users to point to
their own location. Only updates the config.yml file for gitlab-shell,
assumes the user will manage the directory themselves.

Without making it configurable, and always having it set, logging would always be used
and would take up quite a bit of space.

Redis password config

Fixes #729

See merge request !486