[POC] Envoy global rate limit service

[strekm]

Description

Scope of this POC is to get to know possibilities and limitations of Envoy's global rate limit service. Use cases to cover are the same as in previous POC.

Envoy's global rate limit service supports 2 main methods of persistence: memcache and redis. Kyma does not offer in cluster Redis instance and in context of global rate limit Redis should be treated as dependency. In scope of this task explore external Redis support. Explore possibilities and limitations of both external Redis and memcached persistence methods.

Outcome should be documented.

Reasons

DoD:
- [ ] Provide unit and integration tests.

• Provide documentation.
• Verify if the solution works for both open-source Kyma and SAP BTP, Kyma runtime.
  - [ ] If you changed the resource limits, explain why it was needed.
  - [ ] If the default configuration of Istio Operator has been changed, you performed a manual upgrade test to verify that the change can be rolled out correctly.
  - [ ] Verify that your contributions don't decrease code coverage. If they do, explain why this is the case.
  - [ ] Add release notes.

ACs:

• evaluate external Redis
• evaluate external Memcached

Attachments
https://github.com/envoyproxy/ratelimit?tab=readme-ov-file#memcache
part of: kyma-project/api-gateway#1365