Refactor Cells configuration

What does this MR do and why?

Refactor Cells configuration

Important: More context about the refactoring and the plan is found here: #513075 (comment 2360039622)

Addressing: #513075

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. In your GDK, edit your GitLab config/gitlab.yml cell setting by having something like this. Keep the Topology Service config pointing to your existing Topology Service in your GDK

  cell:
    enabled: true
    id: 1
    database:
      skip_sequence_alteration: false
    topology_service:
      address: gdk.test:9095
      ca_file: /Users/omar/gdk/gitlab-topology-service/tmp/certs/ca-cert.pem
      private_key_file: /Users/omar/gdk/gitlab-topology-service/tmp/certs/client-key.pem
      certificate_file: /Users/omar/gdk/gitlab-topology-service/tmp/certs/client-cert.pem

2. In your Rails Console, run something like this Gitlab::TopologyServiceClient::CellService.new.get_cell_info from your Primary GDK Instance. It should return something like this

=> <Gitlab::Cells::TopologyService::CellInfo: id: 1, address: "gdk.test:8080", session_prefix: "cell-1", sequence_range: <Gitlab::Cells::TopologyService::SequenceRange: minval: 1, maxval: 2199023255552>>

3. Edit your config.gitlab.yml by setting cell.enabled to false. Then start Rails Console and run the same command again. You should get something like this

[1] pry(main)> Gitlab::TopologyServiceClient::CellService.new.get_cell_info
NotImplementedError: NotImplementedError

Related to #513075