Put the artifactapi web UI behind Authentik oauth2-proxy (#456)

The artifactapi web UI is open to anyone who can reach the host. Front it with Authentik SSO gated on akP-artifactapi-admin, while leaving the package-manager surfaces (/api/v1, /api/v2, /v2 docker registry, /terraform, /.well-known) untouched — dnf, containerd mirrors, buildah, terraform and CI publish steps cannot do a browser flow.

- Add the oauth2-proxy ConfigMap, Deployment, Service and VMPodScrape.
- Add the oauth-credentials VaultStaticSecret.
- Point the api-route /ui rule at oauth2-proxy and add a /oauth2 rule; the catch-all / rule still goes straight to the api Service on both listeners.

Requires terraform-authentik #34 applied and the Vault kv seed first.

Reviewed-on: #456
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

apps/base/artifactapi/services.yaml

@@ -16,6 +16,26 @@ spec:
   sessionAffinity: None
   type: ClusterIP
 ---
+# Authenticated front door for the web UI only: api-route sends /ui and /oauth2
+# here, oauth2-proxy authenticates and forwards to the ui Service. Every other
+# path reaches the api Service above directly and stays unauthenticated.
+apiVersion: v1
+kind: Service
+metadata:
+  name: oauth2
+  namespace: artifactapi
+spec:
+  internalTrafficPolicy: Cluster
+  ports:
+    - name: http
+      port: 80
+      protocol: TCP
+      targetPort: http
+  selector:
+    app: oauth2
+  sessionAffinity: None
+  type: ClusterIP
+---
 apiVersion: v1
 kind: Service
 metadata: