SMTC-49: Initial stab at defining a registry for the Semantic Properties

[fpddog]

This PR adds the concept of a "registry" as a Pydantic class containing one field per Semantic Property. This is so we can produce a JSON Schema for the registry itself, i.e. a machine readable format that we can then use to ensure the consistency of our component and payload models.

Each property is represented as a type with some extensions (via the usage of Annotated), following the Pydantic mechanisms we've been using so far in the Semantic Core.

I haven't created a new version of the schemas (not worth it until we stabilize these concepts), but I did create a draft which produced:

{
  "$defs": {
    "PoliciesEnum": {
      "enum": [
        "GDPR",
        "CCPA",
        "HIPAA"
      ],
      "title": "PoliciesEnum",
      "type": "string"
    }
  },
  "properties": {
    "is_sensitive": {
      "aspect": "security",
      "description": "Indicates if the field associated with this property contains sensitive data or not.",
      "internal_description": "Sensitive data has some implications that T&S must define.",
      "is_internal": false,
      "title": "Is Sensitive",
      "type": "boolean"
    },
    "data_policies": {
      "aspect": "security",
      "description": "Data policies that apply to the field.",
      "is_internal": false,
      "items": {
        "$ref": "#/$defs/PoliciesEnum"
      },
      "title": "Data Policies",
      "type": "array"
    }
  },
  "required": [
    "is_sensitive",
    "data_policies"
  ],
  "title": "PropertiesRegistry",
  "type": "object"
}