command: Add gdk services list command

What does this merge request do and why?

I wanted to know which services we have, and how many still need to be converted to a real GDK::Services. Add a command that prints the list like this:

Service	Legacy
redis
redis-cluster
minio
postgresql
postgresql-replica
postgresql-replica-2	x
openldap
pgbouncer1	x
pgbouncer2	x
pgbouncer2-1	x
pgbouncer2-2	x
consul	x
postgresql-geo	x
geo-cursor	x
gitlab-workhorse
rails-background-jobs	x
gitlab-k8s-agent	x
gitaly	x
gitlab-ui	x
vite	x
webpack	x
rails-web
gitlab-pages	x
registry	x
grafana	x
prometheus	x
jaeger	x
sshd	x
nginx	x
elasticsearch	x
gitlab-zoekt-indexer-development	x
gitlab-zoekt-indexer-test	x
zoekt-webserver-test	x
zoekt-webserver-development	x
gitlab-docs	x
runner	x
runner	x
runner	x
spamcheck	x
gitlab-ai-gateway	x
gitlab-http-router	x
mattermost	x
snowplow-micro	x
vault

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.