Create a global policy in a project

Creates a new global policy from the supplied policy snapshot JSON. Used by cross-instance promotion to materialize a source proxy's global policy on the target as a standalone, reusable global policy. The policy is created through its policy type's own service and gets that service's checks (a rejected policy returns 400); MCP / A2A policies and the few types without such a service are stored as the import does. Secret fields may be sent as plaintext or as the encrypted value from an export/promotion snapshot: a plaintext value is encrypted before it is stored, an already-encrypted value (or a ${VAR} reference) is stored as is. An AI policy needs the AI Development permission, the others API Management.