Identity-service API: Terms of service retrieval endpoint response is not fully specified

**Link to problem area**: https://matrix.org/docs/spec/identity_service/latest#get-matrix-identity-v2-terms

**Issue**

The schema for `Policy Object` (maybe rename it to `Policies`?) lists only the version field, while from the example it becomes clear that there can be arbitrary other keys, each one containing an object that in turn holds a name and url field.

Start at the GET /_matrix/identity/v2/terms section linked in the issue and compare the Policy Object schema with its example. Update the specification so the schema describes the version field and arbitrary policy entries containing name and url fields, then verify it matches the example.

Written by the indexing model from the issue text.