Add documentation for API authentication with APISIX, OPA, and Keyclo… (#783)

* Add documentation for API authentication with APISIX, OPA, and Keycloak [deploy-test]

* Add knowledge base article on API authentication with APISIX, OPA, and Keycloak

* Update docs/security/authenticatie/apisix-opa-keycloak.md

Co-authored-by: Tom Ootes <tom@ootes.io>

* Update docs/security/authenticatie/apisix-opa-keycloak.md

Co-authored-by: Tom Ootes <tom@ootes.io>

* Clarify policy as code description in API authentication documentation

* Add example APISIX route configuration for API registration

* Add detailed OPA policy and APISIX route configurations for API authentication [deploy-test]

* Refactor API authentication documentation to clarify the roles of APISIX, OPA, and Keycloak in the auth flow

* Update auth architecture diagram [deploy-test]

* Add OPA Keycloak design note [deploy-test]

* Fix auth diagram Mermaid labels

* Trigger deploy test for auth article [deploy-test]

* Fix auth diagram markdown rendering [deploy-test]

* Add tutorial on API authentication with APISIX, OPA, and Keycloak [deploy-test]

---------

Co-authored-by: Tom Ootes <tom@ootes.io>

Author: pasibun

.changeset/clean-keys-flow.md

@@ -0,0 +1,5 @@
+---
+"@developer-overheid-nl/website": patch
+---
+
+Voeg een kennisbankartikel toe over API-authenticatie met APISIX, OPA en Keycloak.

docs/security/tutorials/_category_.json

@@ -0,0 +1,4 @@
+{
+  "label": "Tutorials",
+  "key": "security-tutorials"
+}