Resolve `app/services/snippets/base_service.rb` service response

Why

We have some service response issues here: https://gitlab.com/gitlab-org/gitlab/-/blob/master/.rubocop_todo/gitlab/service_response.yml?ref_type=heads#L30-34

This issue is for app/services/snippets/base_service.rb

What

• research code paths to see if there is any impact on callers. Do they rely on the http_status at all?
• remove entry from .rubocop_todos/
• update service class to use reason instead of http_status
• update specs