Add NetBox OAuth2/OIDC provider + application

NetBox is being deployed to k8s (argocd-apps) with Authentik SSO via
python-social-auth's OpenIdConnectAuth backend. Add the confidential OAuth2
provider/application (client_id netbox, openid/email/profile scopes, strict
redirect to /oauth/complete/oidc/); the client_secret is read from Vault at
kubernetes/namespace/netbox/default/oauth-credentials (the terraform-authentik
runner policy already covers namespace/+/default/oauth-credentials).

Claude-Session: https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv

config/providers_oauth2/netbox.yaml

@@ -0,0 +1,19 @@
+# OAuth2/OIDC provider + application for NetBox
+# (netbox.k8s.syd1.au.unkin.net). client_secret is read from Vault, not committed.
+# NetBox uses python-social-auth's OpenIdConnectAuth backend; its completion URL
+# is /oauth/complete/oidc/.
+name: NetBox
+authorization_flow: default-provider-authorization-implicit-consent
+invalidation_flow: default-provider-invalidation-flow
+client_type: confidential
+client_id: netbox
+client_secret_vault:
+  mount: kv
+  path: kubernetes/namespace/netbox/default/oauth-credentials
+scope_mappings:
+  - goauthentik.io/providers/oauth2/scope-openid
+  - goauthentik.io/providers/oauth2/scope-email
+  - goauthentik.io/providers/oauth2/scope-profile
+redirect_uris:
+  - matching_mode: strict
+    url: https://netbox.k8s.syd1.au.unkin.net/oauth/complete/oidc/