Rate limit technical design

[strekm]

Description

Based on previous POCs and decision to support local rate limiting as part of Istio module provide technical design and API design. This should be focused on use case of local rate limiting but having in mind that later on global rate limiting might be introduced. Technical design should specify additional controller, still being part of Istio module, that will be listening to rate limit CRD.

Main scenario to cover with local rate limit is to protect a workload from overloading. It should be possible to configure number of requests per workload.

ACs:

• technical design of rate limit functionality
• API design for local rate limiting
• above should be extensible to global rate limiting
• ADR created

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.

Attachments
POCs: #774, #826
part of: kyma-project/api-gateway#1365

PR: #930