Add routing rules for Session Prefix

We need to implement the following rules:

• If session cookie matches, it is being classified by Topology Service
• If special force-cell cookie matches, it is classified by Topology Service
• If no match is found it is doing passthrough to defined GITLAB_PROXY_HOST

[
  {
    "match": {
      "type": "cookie",
      "regex_name": "force-cell",
      "regex_value": "^(?<cell_name>cell-\\d+)"
    },
    "action": "classify",
    "classify": {
      "type": "SessionPrefix",
      "value": "${cell_name}"
    }
  },
  {
    "match": {
      "type": "cookie",
      "regex_name": "_gitlab_session(_[0-9a-f]+)?",
      "regex_value": "^(?<cell_name>cell-\\d+)-.*"
    },
    "action": "classify",
    "classify": {
      "type": "SessionPrefix",
      "value": "${cell_name}"
    }
  },
  {
    "action": "proxy"
  }
]

Action Items

• Add the new routing rule to the HTTP Router, see #20 (comment 2020199608)
• Validate on GDK that a logged in user on the 2nd cell have their requests routed to the correct cell. Note: As we do not have login flow yet, we may need to a implement a special rule to force requests to route to the special cell given a special cookie. So that we can get to the login page for Cell 2.
• [Optional] (useful for testing) Configure GDK to add the right session cookie prefix for each additional cell. See here gitlab-org/gitlab-development-kit#2156 (closed) and https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/lib/cell_manager.rb?ref_type=heads#L101 => gitlab-org/gitlab-development-kit#2156 (closed)