[Epic] API Policy Schema - Rate limits

[lgecse]

This enhancement adds a structured, standardized way for the agntcy directory to define and enforce API policies — including rate limits — ensuring consistent governance and interoperability across all directory-managed APIs.

Phase 1 added authz support.

Ratelimit packages:

• https://github.com/uber-go/ratelimit
• https://github.com/envoyproxy/ratelimit