Add session_prefix rules and implement matching cookie for classify

This is based on !232 (merged) and !240 (merged)

• Add src/rules/session_prefix.json for GITLAB_RULES_CONFIG

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

• Now all rules do support match, even for proxy action. For now it only supports cookie match. We can add path match at !223 (merged)
• Extend ClassifyRule for interpolating the matched cookie value into the classify value

TODO:

• Fill details and fully implement it
• Add tests
  • test/index.spec.ts
  • [-] test/rules/classify.spec.ts
  • [-] test/rules/proxy.spec.ts
• Try if it works with GDK

Closes #20 (closed)