Describe the expression-check DSL (paths per point, predicates, operators)

curl --request GET \
  --url https://api-sandbox.featherhq.com/v1/policies/expression-schema \
  --header 'x-api-key: <api-key>'

{
  "predicates": [
    {
      "name": "<string>",
      "signature": "<string>",
      "description": "<string>"
    }
  ],
  "operators": [
    "<string>"
  ],
  "common_fields": [
    {
      "path": "<string>",
      "type": "<string>",
      "description": "<string>",
      "namespace": false
    }
  ],
  "points": [
    {
      "content_paths": [
        {
          "path": "<string>",
          "type": "<string>",
          "description": "<string>",
          "namespace": false
        }
      ]
    }
  ]
}