Envoy Dataplane: API Key

[lgadban]

kgateway version

main

Is your feature request related to a problem? Please describe.

Similar to #12378

API Key AuthN is a missing feature that is common for API gateways.
It is added in #12886 for the agentgateway dataplane but still missing for Envoy dataplane.

Describe the solution you'd like

A working API key AuthN feature implemented natively in the Envoy data plane

Describe alternatives you've considered

https://github.com/Kuadrant/authorino is a possible alternative implementation as an external auth service

Additional Context

• agentgateway: API Key Authentication #12378
  • Initial discussion resulting in merging API key for agentgateway
• https://docs.solo.io/gloo-edge/latest/guides/security/auth/extauth/apikey_auth/
  • ExtAuth based impl in the 1.x Gloo Edge enterprise product:

[ymesika]

EP PR: #12919